A medical light source device worn on the body of an operator enables the application range to be set at a state displaced from the direction in which the body currently faces. An acceleration sensor 106 is attached to a holder 7 to put an illumination section 1 on the body of the operator, and detects a motion of the body of the operator. When an application-range center position setting switch 107b is operated, a position detecting section 108 detects a center position based on the acceleration information detected by the acceleration sensor 106, and an optical axis adjusting section 108 fixes the optical axis of the illumination section 1 to the detected center position. Then, the application angle of application light from the illumination section 1 is capable of being adjusted in a plurality of stages by an application control section 110.