We have developed a fiber optic gyroscope (FOG) using a single mode fiber (SMF) coil and integrated optics (IO), with intermediate-grade performance (bias stability: 3 degrees/hour 1 (sigma) ). Conventional FOGs, which require higher performance than intermediate grade, need polarization maintaining fiber (PMF), an obstacle to cost reduction because of expense. Our unique technique using depolarized light has made it possible to replace the PMF coil with SMF coil, thus reducing cost. This paper describes the FOG configuration we adopted and the test results of our product models that applied this technique under practical environments (temperature, vibration, and magnetic field). We compare the test results of the products using PMF coil.