Provided is an integrated optical current sensor for measuring the magnitude of current. The integrated optical current sensor is fabricated by integrating optical elements, such as a thermo-optic phase modulator, a waveguide polarizer and an optical coupler, on a single substrate. As compared to the known current sensors using optical fibers, the integrated optical current sensor is more compact and enables measurement of current with higher reliability. Provided also is a method for producing current sensor chips in a large scale by using a process for fabricating integrated optical elements.