Tilt sensor housing case and vehicle lamp system

A tilt sensor housing case comprising:

• a main body part comprising a housing space for a substrate on which a tilt sensor is mounted and an opening portion for inserting the substrate in the housing space;
• and
• a lid part configured to close the opening portion,
• wherein the lid part has a first engaging portion extending along an outer surface of the main body part in a state where the lid part is mounted to 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 engaging portion and the second engaging portion, and
• the main body part has a first protrusion and a second protrusion that are positioned to sandwich the first engaging portion between them in a state where the lid part is mounted to the main body part, and each of the first and second protrusions protrudes at least up to the same height as the first engaging portion in a direction in which the outer surface and the first engaging portion are overlapped.