A radar device includes a beat signal generation unit, a first signal processing unit, a second signal processing unit, and a speed determination unit. The first signal processing unit observes beat signals by performing a first number of observations during a first observation time and calculates a first speed from a time series of the beat signals of which number is equal to the first number of observations. The second signal processing unit observes the beat signals by performing a second number of observations during a second observation time and calculates a second speed from a time series of the beat signals of which number is equal to the second number of observations. The second observation time is longer than the first observation time. The time ratio is the ratio of the second observation time to the first observation time. The second number of observations is smaller than the first number of observations multiplied by the time ratio.