In Iwaki City, Fukushima Prefecture, an important prefectural road (Route 26) was blocked by rock fragments from hill slope at 11:00 pm on August 24, 2019. This slope movement was unique in that typical triggering factors, such as heavy rain or an earthquake, did not occur on the day of the event. We performed an urgent field survey on the slope movement on August 27, 2019. The results are as follows : 1) The slope movement occurred on a hillside slope comprising Miocene tuffaceous sandstone and mudstone. The rocks have well developed joint faces and weathering. 2) Blocks “a” and “b” consisted of surface slope failure landforms. The movement directions of the slope failures were controlled by the geological structure, especially dip and strike. Block “c”, located above Blocks “a” and “b”, consists of subsidence landforms. Interviews with residents revealed that artificial caves existed beneath Block “c”. 3) The slope movement involved the subsidence of Block “c” having been induced by roof falling in the artificial caves. The surface slope failures of Blocks “a” and “b” occurred with the subsidence of Block “c”. Rock-cliff Buddha statues occurred on the slope of Block “a” before the slope movement. Photographic material revealed small bedrock displacements in and around the statues. These geological structures suggested that the stress of internal rocks were triggers of the slope movement August 24, 2019.