Japanese mountain rivers are supplied with large quantities of gravel from their tributaries. This paper discusses the relationship between downstream change in gravel size and bed form and the types of gravel transport process along a river's tributaries with steep slope, in order to clarify the influences on gravel supply for main streams from tributaries. Along seven steep slope rivers which are tributaries of the Asahi River in the Asahi Mts. and the Tama River in the Kanto Mts., eastern Japan (Fig. 1 and Table 1), the following features are investigated along each stream (Fig. 3): 1) maximum diameter of river bed gravels, 2) the char-acteristics of bed form, such as the lobate forms on the river bed and falls, and 3) the distribution of the points where gravels are supplied from landslides or small streams. The lobate form is char-acterized by huge gravel, as large as 1 m in diameter, gathered at the front of it and recognized in the convex cross section. Its deposits consist of imbedded and nonsorted material. The rivers are divided into three types of section, named (in order from the upper reaches) the A, B, and C sections, on the basis of maximum diameter and bed form. Each type of section is located in a different range of the channel slope (Table 2). The A section, where the channel slope is steeper than about 200 is characterized by small maximum diameter, many falls, and a few lobate forms. The B section, where the range of the channel slope is generally between 80 and 200‰, is characterized by large maximum diameter and many lobate forms. The C section, where the channel slope is gentler than 80‰ is characterized by small maximum diameter, no falls, and few lobate forms. The A and B sections are found in all of the rivers. In the rivers whose minimum channel slope is steeper than 200‰ the B section is located on a steeper part than the B sections of the other rivers, and the A section extends near the junction with the main stream. The C section is found only in three rivers whose minimum channel slope is gentler than 80‰. Each type of section is formed by a different type of gravel transport process depending on the value of the channel slope, and the influence on gravel supply for the main stream from the tributaries differs according to the type of section located near the junction with the main stream (Fig. 4). The A section is characterized by occurrence and runout of debris flows. The fronts of debris flows, including huge gravels, are swept down this section and only finer particles remain. Many debris flows, which occur in the tributaries where the A section extends near the junction, flow into the main stream. The B section is characterized by deposition of debris flows, and is formed by deposition of de-bris on a long-term basis. Although many of the occured debris flows in the tributaries that have a B section at the junction are deposited in the B section, some of them runout into the main stream. The above-mentioned type of tributaries supply huge gravels to the main stream. Because almost all debris flows are deposited in the B section, in the C section gravels are trans-ported by traction. Therefore none of the huge gravels found in the B section can be transported into the C section. The channel slope at the junction is steeper, so the coarser gravels flow into the main stream from the tributaries that have a C section. This type of tributary supplies no huge gravels for the main stream.