A light source device comprising: a light source; a diaphragm member adapted to adjust light quantity of illumination light supplied from the light source; a diaphragm driving part adapted to drive the diaphragm member to perform an opening operation or a closing operation; an opening/closing control part adapted to set electric energy to be supplied to the diaphragm driving part and to control an opening/closing amount of the diaphragm member; and a control range setting part adapted to detect fixed position information at the time the diaphragm member is fixed at a predetermined position, to set adjustment data for adjusting a drive signal outputted from the opening/closing control part and opening/closing positions of the diaphragm member based on the fixed position information, and to regulate a control range of the opening/closing control part based on the adjustment data; wherein the predetermined position is both a fully opened position and a fully closed position of the diaphragm member, first and second stopper members (24a, 24b) adapted to regulate a maximum rotation range of the diaphragm member are provided at a fully-opened position and a fully-closed position, respectively, characterized in that the light source device further comprises a braking coil for generating induced electromotive force using operation of the diaphragm member and an adjustment circuit for adjusting the induced electromotive force, the control range setting part is adapted to set an output value which is the fixed position information outputted from the adjustment circuit at the time that a position of a rotation range of the diaphragm member is restricted by the stopper member provided at the fully-opened position, as a control range limit value of the fully-opened side of the opening/closing control part, and the control range setting part is adapted to set the output value which is the fixed position information outputted from the adjustment circuit at the time that a position of a rotation range of the diaphragm member is restricted by the stopper member provided at the fully-closed position, as a control range limit value of the fully-closed side of the opening/closing control part, and the control range setting part is adapted to perform adjustment so that the control range limit values are constant values. a light source; a diaphragm member adapted to adjust light quantity of illumination light supplied from the light source; a diaphragm driving part adapted to drive the diaphragm member to perform an opening operation or a closing operation; an opening/closing control part adapted to set electric energy to be supplied to the diaphragm driving part and to control an opening/closing amount of the diaphragm member; and a control range setting part adapted to detect fixed position information at the time the diaphragm member is fixed at a predetermined position, to set adjustment data for adjusting a drive signal outputted from the opening/closing control part and opening/closing positions of the diaphragm member based on the fixed position information, and to regulate a control range of the opening/closing control part based on the adjustment data; wherein the predetermined position is both a fully opened position and a fully closed position of the diaphragm member, first and second stopper members (24a, 24b) adapted to regulate a maximum rotation range of the diaphragm member are provided at a fully-opened position and a fully-closed position, respectively, characterized in that the light source device further comprises a braking coil for generating induced electromotive force using operation of the diaphragm member and an adjustment circuit for adjusting the induced electromotive force, the control range setting part is adapted to set an output value which is the fixed position information outputted from the adjustment circuit at the time that a position of a rotation range of the diaphragm member is restricted by the stopper member provided at the fully-opened position, as a control range limit value of the fully-opened side of the opening/closing control part, and the control range setting part is adapted to set the output value which is the fixed position information outputted from the adjustment circuit at the time that a position of a rotation range of the diaphragm member is restricted by the stopper member provided at the fully-closed position, as a control range limit value of the fully-closed side of the opening/closing control part, and the control range setting part is adapted to perform adjustment so that the control range limit values are constant values.