PURPOSE: To provide a paper cutter having a lock mechanism which enables locking firmly and with a simplification in mechanism.

CONSTITUTION: A spring piece 17 of a paper cutter is locked being mated with a protrusion/recess engaging part and a lock piece 21 is arranged independently on the side of the spring piece 17 to release the locking. A slide mating part 25 is formed at an upper part of the lock piece 21 while a spacer 26 is arranged above the lock piece 21 being allowed to reciprocate in a fixed range. A lock piece fixing part 32 and a lock piece releasing part 33 are formed on the rear of the spacer 26 to make the lock piece 21 move between the locking position and the unlocking position mating with the slide mating part 25 of the lock piece 21 as the spacer 26 shifts.