To provide a device for actuating movable cams for a flat knitting machine, which can simplify a structure for converting the rotation of a motor to the movements of long members in a retractive direction.

A movable cam actuating device X allows a needle raising cam 11 and a rubber cam 12 to be actuated from the outside of a front carriage 1F in response to the movements of a needle raising cam control bar 31 and a rubber cam control bar 32 in a retractable direction via a first and a second actuating members 19 and 20, respectively. The movable cam actuating device X includes: a pinion gear 36 joined to a shaft 351 of a stepping motor 35; a rack gear 37 extending in the traveling direction of the front carriage 1F and meshing with the pinion gear 36; and a joint part 38 joining the rack gear 37 to the control bars 31 and 32. The joint part 38 includes: a shaft part 40 provided on the rack gear 37; and long holes 382 and 392 provided at the other ends of the control bars 31 and 32, respectively, and supporting the shaft part 40 movably in the retractable direction of the control bars 31 and 32 upon the movements of the control bars 31 and 32, respectively, in the retractable direction.