A radar device includes transmission signal generation circuitry that generates one or more transmission signals, a transmission amplifier that amplifies a power level of the one or more transmission signals, a transmission gain controller that adjusts a gain of the transmission amplifier, transmission antenna circuitry that converts each of the one or more amplified transmission signals into each of one or more radio signals and transmit the one or more radio signals to a measurement target space, reception antenna circuitry that receives the one or more radio signals from the measurement target space, and one or more receivers that detect a power level of a transmission/reception leakage signal using the one or more received radio signals. The transmission gain controller adjusts the gain of the transmission amplifier in accordance with a result of comparison between the detected power level and a power level of a transmission/reception leakage signal measured in advance.