Abstract: A correcting device for a typewriter comprises a mount for fixedly mounting the device on the typewriter, a cover member slidably supported from said mount, a cassette containing rotatable feed and take-up spools for feeding and winding up, respectively, type correcting strip, said cassette removably supported from said cover member, said cover member and said supported cassette being moveable on said mount between operative (correcting) and inoperative (normal typing) positions. Ratchet teeth are provided on the take-up spool which cooperate with a lever actuated pawl whereby a segmental movement is imparted to the take-up spool upon depression of a key of the typewriter. A curved cam in cooperative association with the correcting strip roll periphery on the take-up spool are also provided to control movement of the lever so that segmental movement of the take-up spool is substantially uniform regardless of the diameter of the correcting strip roll wound onto the take-up spool.