The gyrometer is comprised of an optical fiber coil (10); an electromagnetic source (12) provided with a separator to supply the coil with two contrarotary waves coming form the source; an interference detector (22) receiving the contrarotary waves; electro-optical phase shifting means (31), which are controlled to provide the waves with a periodical alternating and phase-symmetrical modulation, at 1/2 period τn subtantially equal to the throughput time τf of the coil, and receive a phase shifting ramp of adjustable slope, said means being arranged upstream of the coil for one wave and downstream for the other; and electronic loop and measurement means controlling the direction and the value of the slope of the ramp to cancel the phase shifting of the waves received by the detector. The electronic means are comprised of an analog/digital convertor (27) receiving the output signal from the interference detector (22) and driving a circuit having a digital demodulator (26) receiving a reference signal at the period 2τn, an integrator (28) providing a signal representative of an estimation Φ of the rotation speed, a correction adder (29) and an integrator (30) for the generation of said ramp.