PURPOSE: To enable the appropriateness of data to be easily determined without reference to a factor for a radar reliability drop by comparing Doppler frequencies via the introduction of intermittent CW mode.

CONSTITUTION: In this radar, transmission mode is repeated between FM mode for sending a carrier wave (CW) after modulation with the predetermined modulation signal, and CW mode for sending only the carrier wave. Also, the radar receives a reflection wave from a target, and obtains a signal beating with a transmission transmission wave. In this case, a difference f2 between up and down beat frequencies Fup and Fdn in the FM mode is calculated in a beat frequency difference computation means A, and a deviation between Doppler frequencies fd1 and fd2 in the CW mode is calculated in a Doppler frequency deviation computation means B. In addition, a comparison means C makes a comparison between the deviation and an allowable error variable established with an allowable error setting means D according to measurement accuracy F. Finally, normal and abnormal signals are respectively outputted, according to the extent of the deviation.