An LED light source lamp has built-in drive circuits in a housing, and is used by being attached to a lamp holder. An LED installation plate is arranged, in a main space of the housing, on an attachment side to the lamp holder. An LED module on a surface, of the LED installation plate, opposite to the lamp holder, is a collection of LEDs driven by the drive circuit. A light diffusion member is arranged so as to block the optical axis of light emitted by each LED of the LED module. Here, the drive circuits are arranged in an outer peripheral space, between the LED module and the light diffusion member, so as not to block the optical axis of light emitted by each LED of the LED module.