In industrial devices such as heat exchangers, fuel cells, and chemical reactors, the fluid flow enters the inlet manifold and streams into many branch passages. In order to improve the performance of these devices, it is important to obtain a uniform flow rate distribution in each passage. In the present study, an experimental investigation is performed for multiple-passage duct flows. The multiple-passage duct is a reverse flow type and consists of five branch ducts. The duct flows are investigated from the view-point of flow uniformity and pressure loss. Experiments are performed for Reynolds numbers ranging from 6.0 × 102 to 1.5 ×103, based on the bulk velocity and hydraulic diameter at the inlet duct. The aspect ratio (i.e., the ratio between the height and width of the branch duct) is varied as 0.6, 1.0, and 20. The effect of the outlet manifold volume on the flow distribution is investigated. The wall static pressure is measured, and the pressure loss and flow rate are evaluated. The velocity profiles are measured by a PIV system in order to clarify the effect of the increasing the outlet manifold volume. The results reveal that the flow rate changes only slightly with the aspect ratio. As the Reynolds number increases, the uniformity of the flow rate through each branch duct worsens. A uniform flow distribution is realized by increasing the volume of the outlet manifold. The flow uniformity is related to the reduction of the recirculation region at the inlet manifold.