Provided is a printer capable of reliably combining a main unit and a detachable unit with each other, performing smooth attachment/detachment operation of the detachable unit, easily achieving miniaturization, and suppressing interference with fingertips during the attachment/detachment operation, to thereby increase safety. The printer includes: a main unit (10) including opposed walls (62); and a detachable unit (11) combined with the main unit so as to be attached to/detached from the main unit freely. The detachable unit includes: an engagement pin (50) protruding along an axial line which is non-coaxial and parallel with respect to a platen shaft of a platen roller (5); and a lock pin (51) movable relative to the engagement pin. The opposed walls each include: a first recess (65) and a second recess (66) allowing the engagement pin and the lock pin to be fitted detachably therein, respectively. The engagement pin is incapable of being detached from the first recess when the lock pin is fitted in the second recess, and is capable of being detached from the first recess after the lock pin is detached from the second recess.