A case configured with a base and a cover watertightly contains a circuit board, and a connector housing having a diaphragm is mounted in the circuit board so that the inside and the outside of the case are electrically connected with each other; an outer ring-shaped circumferential wall is provided on the outer surface of the diaphragm, and a protrusion portion having first and second ventilation holes is provided at the side surface of the outer ring-shaped circumferential wall; one end of each of the first and second ventilation holes communicates with the outer surface portion of a water-repellent filter provided on the inner wall surface of the diaphragm, and the other end thereof communicates with the inside of a recess portion that is situated at a side of a mating connector and fits with the protrusion portion.