For a Hall element of a magnetic sensor, a current is caused to pass along a +X-direction and a first voltage is measured in a +Y-direction, a current is caused to pass along the +Y-direction and a second voltage is measured in the +X-direction, a current is caused to pass along a −X-direction and a third voltage is measured in the +Y-direction, and a current is caused to pass along a −Y-direction and a fourth voltage is measured in the +X-direction. Then, a calculation is performed which strengthens effects of Hall voltage mutually and weakens effects of offset voltage mutually based on a value of the first voltage and a value of the second voltage, and the result is compared with a reference value. Furthermore, a calculation is performed which strengthens effects of Hall voltage mutually and weakens effects of offset voltage mutually based on a value of the third voltage and a value of the fourth voltage, and the result is compared with the reference value.