PURPOSE: To prevent bulk materials from being stuck onto wall surfaces of a hopper, control a bridging phenomenon of the bulk materials and smoothen the descending flow of the whole bulk materials in the hopper by forming a part of the inside faces of the hopper, or the front face thereof, with a movable wall capable of moving upward.

CONSTITUTION: A hopper for pellets, having four wall faces (a) to (d), is provided with a discharging rail device 4 at the lower part of a hopper body 1 and, according to the actuation of said device 4, pellets 3 (e.g. kneaded granular material consisting of sludge containing iron, cement and added water) are fed to a subsequent step e.g. a crushing strength measuring device. In this case, a belt conveyor device 2 is provided at a part of the side wall face on the side of the rail device 4 among the side wall faces of the hopper body 1 so as to form a movable wall with an upwardly moving belt 5 having the same width as that of a part of said side wall face. The moving belt 5 is provided in such a manner that its lower end is positioned right above the rail device 4 over the total width thereof while its upper end is projected slightly upward from the level of the top end of the hopper body 1. As a result, a bridging phenomenon of the pellets in the hopper can be prevented.