A supporting means of a trough has a lever assembly with a base lever and a vibration lever respectively rotatably connected together at lower ends thereof by a common connecting shaft. The base lever is rotatably supported through a first shaft by a frame. The vibration lever is rotatably connected through a second shaft with the trough. The vibration lever is swingably held through spring means by the base lever. The direction in which the object on the trough is conveyed is reversed by rotating the lever assembly partly around the first shaft of the base lever so as to change the angle of inclination of the lever assembly with regard to the lengthwise direction of the trough between a first angle “A” at which the object on the trough moves in a certain direction and a second angle “B” at which the object moves in an opposite direction.