A light source device (100) includes a semiconductor light source (131, 132, 133), a light source control section (114), an optical sensor (141, 142, 143), a sensor control section (112), and an intensity adjusting section (115). The light source control section (114) controls a light quantity per field of light to be emitted from the semiconductor light source, by pulse width modulation. The optical sensor (141, 142, 143) receives the light emitted from the semiconductor light source to acquire a quantity of the received light. The sensor control section (112) controls the optical sensor to detect the light in an exposure period shorter than a minimum pulse width in the pulse width modulation, thereby acquiring the quantity of the received light which is acquired by the optical sensor. The intensity adjusting section (115) adjusts emission intensity of the semiconductor light source on the basis of the quantity of the received light.
