A front end 7 of a locking arm 4 provided on a rear holder 1 is inserted into a hole portion 25 formed in a main housing 21, and the locking arm 4 is supported like as a bridge. The main housing 21 is inserted into a hood portion 44 of a cooperating housing 41 and connecting terminals are connected to each other to establish the electrical connection. A locking claw 5 formed on the locking arm 4 is once resiliently moved downward to pass through a locking claw 43 of the cooperating housing 41 and is then restored into an original posture to engage the locking claw 5 with the locking claw 43. Once the main housing 21 is engaged with the cooperating housing 41, these housings could not be released accidentally.