To improve the workability of assembling and fixing of a lamp by facilitating attachment and exchange of an installing seat and preventing breaking away, in a vehicular interior lamp equipped with the installing seat in a screw insertion hole provided on a lamp body and fixed to a vehicular body panel with a screw.

The installing seat 3 is provided with a fitting portion 31 having outer diametrical measurements generally equal to the inner diametrical measurements of the screw insertion hole 18 and having axial length generally equal to the wall thickness of a lamp body, a seat surface portion 32 adjoining an axially rear end side of the fitting portion 31 and having outer diametrical measurements larger than the inner diametrical measurements of the screw insertion hole 18, and a locking portion 33 adjoining an axial tip end side of the fitting portion 31 and having outer diametrical measurements larger than the inner diametrical measurements of the screw insertion hole 18. On a part of the circumference of the installing seat 3, a notch that can decrease the diameter of the installing seat 3 is formed in the axial direction including the seat surface portion 32, the fitting portion 31, and the locking portion 33.