This invention relates to a device for mounting a printing type array on a printer. The mounting device comprises a pin supported on the casing of a printing type array for moving into and out of a hole in the printing type array under and against resilient force, respectively, a pressure member secured to the machine framework for urging the pin into the hole in the printing type array, a motor movably supported on a carriage and having a rotary shaft including a flange and a latch pin normally subjected to resilient force to protrude from one face of the flange and retract from the one face of the flange against resilient force and resilient retainer means on the motor rotary shaft and printing type array for preventing the printing type array from moving in the axial direction of the shaft as the motor moves to the operative position and for allowing the printing type array to rotate together with the shaft as the shaft rotates.