To solve the problem of incompatibility between an LED of a light source and an incandescent bulb such as S-bulb of an existing vehicular light fixture.

The vehicular lighting fixture comprises a lamp housing 2 and lamp lens 3, a socket 4 to which a base 15 of an incandescent bulb 14 is detachably fitted by rotating and is electrically connected, and a light source unit 5 that comprises a semiconductor light source 31, a light source housing 32, and a base 34 that has a similar construction to that of the base 15 of the incandescent bulb 14. The surface which faces the socket 4 of the light source housing 31 is provided with a contact boss for suppressing looseness, and for vibration isolation that reduces play and vibration blurring against the socket 4 of the light source unit 5 by contacting to the socket 4 when the light source unit 5 is attached to the socket 4.