An illuminating device includes: a semiconductor light source； a temperature control unit disposed on the light source for controlling a temperature of the light source to a desired temperature； a dew condensation determination unit for determining whether dew condensation may occur based on at least a temperature associated with the illuminating device and an ambient environment condition of the illuminating device； and a temperature control mode selection control unit for selecting, as a temperature control mode of the temperature control unit, a dew condensation suppression mode in which the temperature control unit has a temperature higher than a predetermined temperature and equal to or less than an upper limit of a usable temperature of the light source, based on priority items of operational control of the illuminating device and characteristics of the light source, to temperature-control the temperature control unit, when the determination unit determines that dew condensation may occur.
