According to one embodiment, a sensor device includes a transmitter part, a receiver part, a signal generation part, and a determination part. The transmitter part is configured to emit a radio wave outside as a transmission wave. The receiver part is configured to receive a reflection wave reflected by an object as a reception wave. The signal generation part is configured to generate a first output signal generated based on the transmission wave and the reception wave, a second output signal provided with a phase different from that of the first output signal, and a third output signal generated based on the first output signal and the second output signal. The determination part is configured to determine presence or absence of an object based on the first output signal, the second output signal, and the third output signal.