Abstract: An engaging structure of a flexible retainer which includes a retaining portion for retaining a member to be retained and which retains the member to be retained at a mounting plate by engaging the retaining portion with a mounting hole formed at a mounting plate, comprising: a pair of leg pieces which are inserted through the mounting hole; a pair of pawl pieces which are provided at an anchor portion to which distal ends of the pair of leg pieces are connected and which are inserted through the mounting hole so as to elastically abut a back surface of the mounting plate; and elastic plates which are provided in pairs so as to oppose the pawl pieces and elastically contact the surface of the mounting plate. Because the elastic plates urge the anchor portion in a direction of withdrawing the anchor portion, the engaging structure of the retainer can conform to changes in the thickness of the mounting plate.