An information processing apparatus for executing information processing on a sheet material using a head member arranged for information processing area comprises a head mounting member for mounting a head member thereon, this head mounting member having a position for attaching and detaching the head member to and from the head mounting member, and a mounting position to mount the head member on the head mounting member by positioning the head member with respect to the head mounting member; a pressing member movably arranged on the head mounting member, this pressing member abutting upon the head member mounted on the head mounting member to cause the head member to shift from the attaching and detaching position to the mounting position by the application of pressure given to the head member; and a contact area for the pressing member and head member to abut upon each other, this contact area being arranged to reduce slide resistance to occur in the direction different from the direction in which the head member shifts from the attaching and detaching position to the mounting position. With this structure, the slide resistance to be exerted between these members, which may produce adverse effect on positioning the head member, is made extremely small in order to reliably position the head member exactly.