A tilt sensor housing case includes a main body part including a housing space and an opening portion and a lid part configured to close the opening portion. The lid part has a first engaging portion extending along an outer surface of the main body part. The main body part has a second engaging portion on the outer surface corresponding to the first engaging portion. The lid part is mounted to the main body part by a snap-fit coupling using the elasticity of the lid part and locked to the main body part by the engagement of the first and second engaging portions. The main body part has a first protrusion and a second protrusion that are positioned to sandwich the first engaging portion between them, and each of the first and second protrusions protrudes at least up to the same height as the first engaging portion.