PURPOSE: To obtain a photocurrent sensor, which can measure the magnetic fields in three-dimensional directions at the same time, by acquiring three outputs from one incident light.

CONSTITUTION: The first ray emitting surface is present in the orthogonal direction with respect to the ray incident surface of a first polarizer 5a. A first analyzer 7a is arranged for the first ray emitting surface through a first magnetooptic crystal 6a. The second ray emitting surface is present in the orthogonal direction with respect to the first ray emitting surface of the first polarizer 5a. A second polarizer 5b is arranged for the second ray emitting surface through a λ/4 plate 10. The fourth ray emitting surface is formed in the second polarizer 5b. The emitting directions of the fourth ray emitting surface are orthogonal to the ray, which is emitted from the second ray emitting surface, the rays, which are emitted from the third ray emitting surface and the second ray emitting surface so that the directions of the emitted lights are in parallel, and the ray, which is emitted from the first ray emitting surface. A second analyzer 7b is arranged for the third ray emitting surface through a magnetooptic crystal 6b. A third analyzer 7c is arranged for the fourth ray emitting surface through a third magnetooptic crystal 6c.