A printing apparatus wherein a platen for supporting a recording medium printed by a print head is pivotally supported by a support member. The support member, which extends between left and right side frames of the printer, includes a first and a second engaging portion at its opposite ends. These engaging portions respectively engage an aperture and a cutout formed through the respective side frames, so that the support member and the platen are pivotally supported by the side frames. The cutout is aligned with the aperture, and is open at an edge of the corresponding side frame. This side frame includes a detent portion disposed adjacent to the cutout. The support member further includes a third engaging portion which engages the detent portion, thereby preventing the second engaging portion from being disengaged from the cutout through the open end of the cutout.