A white light of a lamp which can flash is passed through a rotary filter fitted with a plurality of color filters to output colored lights of a field sequential type. An output signal of a color filter detecting device, detecting the timing when the color filters are interposed in a light path, is used to produce trigger signals different in the delay amount. The light emitting timing of the lamp is delayed relatively from the time when the color filters are interposed in the light path to control the emitted light amounts of the colored lights.