A moving body detection device comprising: an oscillation circuit configured to output an oscillation signal having a predetermined frequency; a transmitter configured to transmit to a monitoring space a continuous energy wave whose amplitude changes periodically based on the oscillation signal that is outputted from the oscillation circuit; a receiver configured to receive a reflected wave that is generated by the continuous energy wave being reflected by an object that exists in the monitoring space, and output a reception signal; a phase detection portion configured to mix the oscillation signal and the reception signal to obtain a Doppler signal that depends on a frequency difference between the oscillation signal and the reception signal; a moving body determination portion configured to detect a moving body in the monitoring space by performing signal processing on the Doppler signal, and output a detection signal; and a control portion configured to periodically switch between a halt mode of causing at least the transmitter and the phase detection portion to halt and a detection mode of causing the transmitter and the phase detection portion to operate, the control portion being configured to, in the detection mode, determine whether or not the Doppler signal is outputted from the phase detection portion in a period from a point of time when a predetermined waiting time elapses from a start point of the detection mode until the detection mode ends, characterised by the control portion being configured to, upon determining that the Doppler signal is outputted, extend the detection mode for the transmitter and the phase detection portion and switch the moving body determination portion from a halt state in which the moving body determination portion is caused to halt, to an operating state in which the moving body determination portion is caused to operate, and upon determining that the Doppler signal is not outputted, switch to the halt mode for the transmitter and the phase detection portion. an oscillation circuit configured to output an oscillation signal having a predetermined frequency; a transmitter configured to transmit to a monitoring space a continuous energy wave whose amplitude changes periodically based on the oscillation signal that is outputted from the oscillation circuit; a receiver configured to receive a reflected wave that is generated by the continuous energy wave being reflected by an object that exists in the monitoring space, and output a reception signal; a phase detection portion configured to mix the oscillation signal and the reception signal to obtain a Doppler signal that depends on a frequency difference between the oscillation signal and the reception signal; a moving body determination portion configured to detect a moving body in the monitoring space by performing signal processing on the Doppler signal, and output a detection signal; and a control portion configured to periodically switch between a halt mode of causing at least the transmitter and the phase detection portion to halt and a detection mode of causing the transmitter and the phase detection portion to operate, the control portion being configured to, in the detection mode, determine whether or not the Doppler signal is outputted from the phase detection portion in a period from a point of time when a predetermined waiting time elapses from a start point of the detection mode until the detection mode ends, characterised by the control portion being configured to, upon determining that the Doppler signal is outputted, extend the detection mode for the transmitter and the phase detection portion and switch the moving body determination portion from a halt state in which the moving body determination portion is caused to halt, to an operating state in which the moving body determination portion is caused to operate, and upon determining that the Doppler signal is not outputted, switch to the halt mode for the transmitter and the phase detection portion.