A battery-powered light source device 5 has an DC/DC converter 61 that boosts the supply voltage of a battery 51 and supplies electrical power to a lamp 31, and, inside this DC/DC converter 61, are provided a comparator 65 that compares a specific reference voltage to the output voltage of a DC/DC converter 61, and a control component 66 that keeps the output voltage from the DC/DC converter 61 at a specific lamp voltage on the basis of the comparison result of this comparator 65, whereby the supply voltage of the battery 51 is boosted and the optimal lamp voltage is obtained. Consequently, the battery-powered light source device 5 allows the brightness of the lamp to be adjusted and a high step-up efficiency to be obtained, and the battery can therefore be used more efficiently, and a more convenient use of the endoscope is possible.