A printing unit, comprising: a head unit including a thermal head configured to perform printing on a recording sheet; a platen unit which is detachably combined with the head unit, and includes a platen roller configured to convey the recording sheet; a fixed blade provided on one of the head unit and the platen unit; and a movable blade provided on another one of the head unit and the platen unit so as to be movable relative to the fixed blade, wherein the another one of the head unit and the platen unit includes: a rack member coupled to the movable blade so as to be movable integrally with the movable blade; a drive mechanism which includes a drive pinion allowed to mesh with the rack member, and is configured to move the movable blade between a standby position at which the movable blade is away from the fixed blade and a cutting position at which the movable blade climbs over the fixed blade; and a return mechanism which includes a return pinion allowed to mesh with the rack member, and is configured to move the movable blade from the cutting position to the standby position side under a state in which the movable blade is stopped at the cutting position, wherein the rack member includes: a drive rack including a plurality of drive rack teeth to mesh with the drive pinion; and a return rack which is formed independently of the drive rack, and includes a plurality of return rack teeth to mesh with the return pinion, wherein the drive rack and the return rack are provided side by side, and characterized in that the plurality of drive rack teeth of the drive rack and the plurality of return rack teeth of the return rack are different from each other in at least one of a phase aspect or a pitch aspect. a head unit including a thermal head configured to perform printing on a recording sheet; a platen unit which is detachably combined with the head unit, and includes a platen roller configured to convey the recording sheet; a fixed blade provided on one of the head unit and the platen unit; and a movable blade provided on another one of the head unit and the platen unit so as to be movable relative to the fixed blade, wherein the another one of the head unit and the platen unit includes: a rack member coupled to the movable blade so as to be movable integrally with the movable blade; a drive mechanism which includes a drive pinion allowed to mesh with the rack member, and is configured to move the movable blade between a standby position at which the movable blade is away from the fixed blade and a cutting position at which the movable blade climbs over the fixed blade; and a return mechanism which includes a return pinion allowed to mesh with the rack member, and is configured to move the movable blade from the cutting position to the standby position side under a state in which the movable blade is stopped at the cutting position, a rack member coupled to the movable blade so as to be movable integrally with the movable blade; a drive mechanism which includes a drive pinion allowed to mesh with the rack member, and is configured to move the movable blade between a standby position at which the movable blade is away from the fixed blade and a cutting position at which the movable blade climbs over the fixed blade; and a return mechanism which includes a return pinion allowed to mesh with the rack member, and is configured to move the movable blade from the cutting position to the standby position side under a state in which the movable blade is stopped at the cutting position, wherein the rack member includes: a drive rack including a plurality of drive rack teeth to mesh with the drive pinion; and a return rack which is formed independently of the drive rack, and includes a plurality of return rack teeth to mesh with the return pinion, a drive rack including a plurality of drive rack teeth to mesh with the drive pinion; and a return rack which is formed independently of the drive rack, and includes a plurality of return rack teeth to mesh with the return pinion, wherein the drive rack and the return rack are provided side by side, and characterized in that the plurality of drive rack teeth of the drive rack and the plurality of return rack teeth of the return rack are different from each other in at least one of a phase aspect or a pitch aspect.