PURPOSE: To minimize the time lag from the energization of a motor till the push out of a piston body by driving a pressing means without increasing motor load and braking the same when inertial force acts in the direction where said means retreats.

CONSTITUTION: The inertial force of the pressing means 3 which is retreated by the internal pressure remaining in the viscous material in a cartridge 1 of a viscous material disperser constituted to advance the pressing means 3 for pressing the piston body 2 by the driving power of the decelerated motor is braked by an elastic ring body. On the other hand, a clutch lever 31 is disengaged at the same instant when the piston body 2 is pressed and stopped upon turning off of an energizing switch 29 by a trigger 27. The pressing means 3 is then freed by a clutch plate 53-decelerating means 4-wire 5, by which the pressing means 3 is slightly retreated to prevent the backward sagging. The time lag till the start of pushing out the piston body is thus minimized in the restarting stage.