In a fitting confirmation construction, a lock arm is provided in a housing of a first connector. The lock arm includes a lock wall inclined and disposed at a front end of the lock arm in a direction from the first connector toward the second connector; a deflection space formed at a rear of the lock wall in the direction; and an operation plate disposed on the deflection space. A confirmation opening is provided in a rear wall of the housing, and has a height equal to a height of the deflection space. A lock projection is provided on a second connector to be brought into engagement with the lock wall. A rear end face of the operation plate is exposed to a rear outside of the housing of the first connector through the confirmation opening, only in a state where the lock arm is deflected.