An endoscope light source device to which a connection portion of an endoscope is detachably attached includes a light source section that radiates primary light that enters an entrance end in the connection portion, a positioning member that positions the entrance end on a center axis of the primary light from the light source section when the connection portion is arranged in the light source device, and a pressing member that presses the connection portion toward the positioning member after the connection portion is arranged in the positioning member. The light source device further includes a heat transmission member that functions as at least one of the positioning member and the pressing member, and transmits heat generated from the connection portion.