PURPOSE: To attempt compact construction an higher reliability, by detecting earth magnetism with a detecting unit and detecting its direction on the basis of outputs of then obtained respective processing circuits.

CONSTITUTION: For this sensor, an approximately annular arrangement of a zero-magnetostriction amorphous wires AF is adopted with, for instance, 3 cores of high magnetic permeability set inside a carrier 5 excavated with a ring-shaped groove and, the sensor is composed of a detecting unit 1 wound with coils 3 (3A, 3B), 4 (4A, 4B) respectively in 4 points of the amorphous wire AF corresponding to the intersecting points of X- and Y-axes of the vertical co-ordinate system and processing circuits 2A, 2B obtaining X-direction output E01 and Y-direction output E02 by processing respectively the outputs from respective coils 3 and 4, and in this sensor, each detecting unit 1 driven by the driving frequency set by the circuits 2A, 2B and difference of magnetic field intentities generated in the respective coils 3, 4 is detected by the respective circuits 2A, 2B to be taken out as outputs E01, E02 through an active filter. Thus, compact construction and improvement of reliability can be attempted.