When male and female housings are attached to each other, a side projection of a locking arm contacts and presses a side engaging part to bend the locking arm in a specific amount and overlap a side projection of the locking arm with a projection of the male housing. At this time, a main engaging part contacts and presses downward a main projection of the locking arm. Then, since the projection of the male housing is under the side projection, the locking arm is temporarily supported at both sides and bent in a bow shape vertically. Then, after the male housing is inserted into the female housing further, the bend of the locking arm is released, and simultaneously the main projection and the main engaging part engage with each other to complete the attachment between the male and female housings.