A connector housing mounting structure includes a connector housing; and a mounting member having a mounting surface. The connector housing includes a housing body, and a pair of flange portions extending from the housing body and having first mounting holes respectively. The mounting member includes a pair of first columnar portions protruding in parallel with each other from the mounting surface. Each of the first columnar portions is inserted into each of the first mounting holes, and the pair of flange portions is fixed to the mounting surface, thus the connector housing is regularly mounted on the mounting surface. A size of one of the flange portions in a width direction perpendicular to an extending direction of the flange portion is larger than the other flange portion in order that in case of incorrect mounting, the larger flange becomes obstructed and forms a visible indicator of misinstallation.