A fiber-optic gyroscope having a single mode fiber coil for sensing the rotation suffers from drift or fluctuation of scale factor of the output signals owing to spontaneous rotation of polarization of beams propagated in the fiber coil. Thus, two depolarizers are required in front of and at the back of the polarizer to avoid the fluctuation. The depolarizer of prior art consists of two birefringent materials twistedly connected with each other at an about 45.degree. inclination angle between the principal axes of one and the principal axes of the other. A conventional fiber-type depolarizer has two polarization maintaining fibers connected together. A new, simplified depolarizer is proposed. The depolarizer is built by gluing a polarization maintaining fiber to an end of the polarizer with an about 45.degree. inclination angle between the principal axes of the fiber and the principal axes of the polarizer. The depolarizer allows us to dispense with one polarization maintaining fiber and spare the operation for connecting fibers by once.