PURPOSE: To enable a device to continuously force fluid to be fed from a delivery port through the other end of a helical groove, by circulating a ball, fitted to the helical groove, to run along a forced feed passage through rotation of a screw and transferring the fluid, introduced to one end of the forced feed passage, while the fluid is pressed by said ball.

CONSTITUTION: If a ball 12, fitted to a helical groove 4, moves respectively along a forced feed passage 11 in accordance with rotation of a screw 3, working fluid in an actuator 22, being allowed to flow passing through a start end 4a of the helical groove 4 from a suction part 17, is introduced into the forced feed passage 11 in a rear side in the moving direction of the ball 12. If the helical groove 4 is again aligned to a part just below one end of a return passage 14, the next ball 12 is fitted to the helical groove 4, and forced feed device, holding the working fluid longitudinally between the balls 12 by its movement in the right direction, transfers the fluid in the right direction in the forced freed passage 11. In this way, the device, being of construction bringing the ball 12 into contact with the forced feed passage 11, decreases friction resistance in a contact part, and the device, enabling the ball 12 to be moved at a high speed and suppressing a reverse flow of the working fluid to a minimum limit, can continuously deliver the working fluid from a delivery port 18.