To permit a male connector to surely recede within a connector holder without need for great pressing force after completion of fitting of a connector.

A male connector 10 has an engaging piece 28 capable of changing positions between a position for inhibiting receding of the male connector 10 within a connector holder 14 and a position for permitting the receding. A female connector 12 has an elastic arm 46 elastically deformed by a removal preventing frame 36 for the male connector in the course of fitting with the male connector 10 and released from the removal preventing frame 36 to return to its original state when the fitting is completed. In the course of the fitting of the male connector 10 with the female connector 12, the engaging piece 28 retains the position for inhibiting receding to inhibit the receding of the male connector 10 within the connector holder 14. When the fitting between both connectors 10 and 12 is completed, the position of the engaging piece 28 is changed to the position for permitting the receding by resilience at the time the elastic arm 46 returns from the elastically deformed state to its original state to permit the male connector 10 to recede within the connector holder 14.