To provide a waterproof construction of a head lamp a vehicle which prevents a fit part of a waterproof cover from being dislocated through being pushed strongly by a user, and waterproof performance from being lowered.

In a waterproof construction of a tiltable reflector 2 attached in a lamp housing 1, a fit part 11 is covered by a slip-off prevention piece 14 to prevent waterproof performance from deteriorating by the fit part 11, in particular, of a waterproof cover 7 being pushed by a user. The slip-off prevention piece 14 is provided on the periphery of a socket cover 12 to decrease the number of part items. Further, by using a flange part provided on a bulb socket as a slip-off prevention piece in place of the slip-off prevention piece 14, a simpler and smaller-sized luminaire for use in a vehicle having designing flexibility can be provided and also benefit in cost can be desired.