To precisely control a polarized wave front of light propagated through a sensor fiber in an optical fiber current sensor and a current measuring method using the optical fiber current sensor.

This optical fiber current sensor includes a polarized wave control means 40 constituted of a Faraday element 41, and a magnetic field generation means 42 for applying a magnetic field to the Faraday element 41, and is provided further with a magnetic field regulation means 421 for regulating a magnetic field Hctrl generated from the magnetic field generation means 42. The magnetic field Hctrl is regulated to control thereby the polarized wave front of the linear polarized light incident into the first sensor fiber 11 for measuring a current I to be measured.