PURPOSE: To provide a fixing structure without requiring much labor for fixing, enabling fixing even in a narrow part, and without generating loosening, in fixing a base of a stop lamp and the like to an arm of variable angle.

CONSTITUTION: A locking part 22 consists of a knurled part 22a and a top split pin 22b whose tip is thinner than its root part, and the size of the locking part is machined according to the knurled hole 20a of the base 20 and the press-in hole 21b of an arm 21. Fixing is carried out by inserting the locking part 22 from the base 20 side with the direction of a claw of the pin 22b meeting the press-in hole 21b, so that the knurled part 22a of the locking part 22 engages with the knurled hole 20a, and at the same time the pin 22b is pressed into the press-in hole 21b. Fixing is thus completed only by inserting the locking part 22 without generating loosening.