To provide a portable light source device little affected by changes of outside air temperatures and capable of providing extremely high output stability.

A deuterium lamp 10 of this portable light source device is housed in a lamp box 42, and further, is housed in a case 41 so as to minimize effects from changes of outside air temperatures. The deuterium lamp 10 which is sensitive to temperature changes is covered not only by the lamp box 42 but also by the case 41 so that the lamp is housed with a double shield structure. A radiating fin 83 is extended between the lamp box 42 on a front side and a cooling fan 43 on a back side in the case 41 so that cooling air is generated along the radiating fin 83 and the cool air entering in the case 41 is emitted outside swiftly by the cooling fan 43. Therefore, efficiency of exchanging air in the case 41 is improved and warm-up time necessary for stabilizing output at a time of starting a lamp is shortened.