An illumination unit includes semiconductor light sources, a target light quantity setting unit for setting a target light quantity for a total outgoing light quantity, a light quantity ratio setting unit for setting an outgoing light quantity ratio among the semiconductor light sources, an amplitude value setting unit for setting amplitude values of driving signals for the semiconductor light sources based on the set outgoing light quantity ratio and a driving signal generating unit for generating the driving signals by use of common pulse modulation control while keeping the set amplitude values. When the target light quantity is set, a driving pulse signal corresponding to the target light quantity is set in common among the semiconductor light sources. The driving pulse signal is formed to have amplitude values corresponding to the outgoing light quantity ratio to generate individual driving signals for driving the semiconductor light sources respectively.
