An object of this invention is to provide a modulator, an optical transmitter and an optical transfer device which can modulate a channel signal while suppressing residual AM signals regardless of the frequency of a channel signal and suppressing deterioration of the channel signal due to impossibility of giving a sufficient FM demodulation amplitude. A modulator 2 according to this invention is a modulator 2 for modulating an input signal, comprising: a branching circuit 21 for producing an inverted signal with an inverted phase of the phase of a first input signal transferred within a first frequency bandwidth; a first semiconductor laser 22a for FM-modulating the first input signal to produce a first FM-modulated light beam; a second semiconductor laser 22b for FM-modulating the inverted signal to produce a second FM-modulated light beam; an optical phase-modulating unit 23 for changing the phase of one of the first FM-modulated light beam and the second FM-modulated light beam on the basis of a second input signal transferred within a second frequency bandwidth, thereby producing a phase-modulated light beam; an optical merging unit 24 for merging the other of the first FM-modulated light beam and the second FM-modulated light beam and the phase-modulated light beam thereby to produce a modulated light beam; and a photoelectric converting unit 25 for converting the modulated light beam in a modulated signal through optical heterodyne detection.