A detection device includes: a first correlation circuit that computes correlation of a first wave detection signal, which is a phase-modulated input wave detected at determined frequency, with a determined code sequence for every code composing the determined code sequence, and to generate first correlation signals the number of which corresponds to a code sequence length, which is a length of the determined code sequence; and a control circuit that rotates phases of the first correlation signals, generates an added value by adding the phase-rotated first correlation signals, and determines based on the added value whether the phase-modulated input wave is a return wave from a determined object.