To provide a light source device capable of stably and efficiently outputting a large quantity of light.

The light source device comprises a plurality of light source elements arranged on an annulus ring and pulse-lighted sequentially toward the center axis of the annulus ring to emit illumination light; a light guide part rotatably arranged on the center axis and having an incidence plane which the illumination light emitted from the light source elements enter, and a reflecting surface for reflecting the incident illumination light in a direction along the center axis; and a driving means for controlling a pulse lighting phase range which is a lighted period of the light source elements according to the rotational phase of the light guide part. When the pulse lighting phase range W is short with respect to a maximum pulse phase range M which is the longest period when the illumination light emitted from the light source elements enters the incidence plane, the driving means controls the pulse lighting phase range W to provide a pre-light-out phase range F and a post-light-out phase range R which are the periods when the light source elements are put out, before and after the pulse lighting phase range W in the maximum pulse phase range M.