The object of the invention is to provide a rotational angle measurement apparatus that is capable of correcting an error due to pin-angle error with a small amount of calculation operation. The rotational angle measurement apparatus includes a magnetic sensor 301 and a signal processing unit 303M. The magnetic sensor includes two bridges comprising magneto-resistance elements each having a pinned magnetic layer. A ratio-calculation unit 381 of the signal processing unit 303M calculates a ratio Vy/Vx of output signals Vx and Vy. A parameter correction unit 382 subtracts a predetermined correction parameter β from the ratio Vy/Vx calculated by the ratio-calculation unit. An a tan-processing unit 383 conducts arctangent processing on the value calculated by the parameter correction unit and calculates an angle of magnetic field θ.