A lock structure of a connector includes a lock arm and a lock release arm which are provided in one connector housing of a pair of connector housings which are fitted into each other. The lock arm is engaged with a lock engagement part of the other connector housing to lock a fitting state between the connector housings when fitting between the connector housings is completed. The lock release arm is formed integrally with the lock arm and can deflect the lock arm in a lock release direction. The lock release arm is provided above the lock arm.