A sensor mounting structure for mounting sensors onto sensor mounting portions formed on a case body includes: an elastically deformable mounting flat spring mounted on the case body so as to cover outer surface part of the case body, allowing the sensors to be mounted on the sensor mounting portions by pressing the sensors from outside. The mounting flat spring includes sensor pressing portions for pressing the sensors, a pair of pressed portions being pressed in directions nearing each other from outer surface sides by predetermined members, and engaging portions for engaging with the case body in a direction orthogonal to the directions in which the pressed portions are pressed.