PROBLEM TO BE SOLVED: To make magnetic field measurement in multiple directions possible in an optical pump type magnetometry, although probe light is monodirectional.SOLUTION: In a magnetic field measurement device 1, a light source 18 irradiates a gas cell 12 with a linear polarized light serving as both a pump light and a probe light in the direction of axis Z, a magnetic field generator 8 applies, to the gas cell 12, alternating magnetic fields that are the same in cycle and differ in phase in each of directions of axes X and Y. An arithmetic control unit 30 calculates the magnetic field C (C, C, C) of a measurement area using the X, Y-axis components A, Aof the alternating magnetic fields and a spin polarization degree Mthat is equivalent to the measured value Wof a magnetometric sensor 10.SELECTED DRAWING: Figure 1【課題】光ポンプ式の磁気計測において、プローブ光が一方向でありながら、複数方向の磁場を計測可能とすること。【解決手段】磁場計測装置１において、光源１８は、ガスセル１２に対して、ポンプ光とプローブ光とを兼ねた直線偏光をＺ軸方向に照射し、磁場発生器８は、ガスセル１２に対して、Ｘ，Ｙ軸方向それぞれに、同一周期であり且つ位相が異なる交番磁場を印加する。演算制御部３０は、交番磁場のＸ，Ｙ軸方向成分Ａx，Ａyと、磁気センサー１０の計測値Ｗ-に相当するスピン偏極度Ｍxとを用いて、計測領域の磁場Ｃ（Ｃx，Ｃy，Ｃz）を算出する。【選択図】図１
