A magnetic sensor for borehole magnetometer includes an upper-opened pipe-shaped housing; a frame installed at an inside of the housing; an upper-opened magnetic sensor part installed at a bottom side of the frame; a lid covering the opened upper side of the magnetic sensor part; and a magnetic sensor disposed at an inside of the magnetic sensor part to measure a magnetic force, wherein an upper side and a bottom side of the magnetic sensor is respectively installed with a spring, a bottom side of the lid and the magnetic sensor part are formed with a fixing groove for fixing an upper spring and a bottom spring each installed at an upper side and a bottom side of the magnetic sensor.