A modulation error measurement device according to the present invention receives a demodulated signal containing a demodulated I signal and a demodulated Q signal from a quadrature demodulator receiving an RF signal output by a quadrature modulator and applying the quadrature demodulation to the received RF signal, and measures a quadrature error corresponding to a phase difference between an I component and a Q component of the modulated signal. The quadrature modulator applies quadrature modulation to an original I signal (ω1) and an original Q signal (ω2) having frequencies different from each other. The modulation error measurement device includes an I-frequency-phase deriving unit 14I which derives the phase of a component of an I frequency (ω1) of the demodulated signal, an opposite-sign I-frequency-phase deriving unit which derives the phase of a component of an opposite-sign I frequency (−ω1) of the demodulated signal, a Q-frequency-phase deriving unit which derives the phase of a component of a Q frequency (ω2) of the demodulated signal, and an opposite-sign Q-frequency-phase deriving unit which derives a phase of a component of an opposite-sign Q frequency (−ω2) of the demodulated signal.