A steering angle detection device includes: a shaft angle detector that detects a rotation angle of a shaft that transmits a rotation operation of a steering member to a steering mechanism a motor angle detector that detects a rotation angle of a motor that applies a steering assist force to the steering mechanism a steering angle calculation unit that calculates a steering angle on the basis of a combination of the rotation angle detected by the motor angle detector and the rotation angle detected by the shaft angle detector, and a temperature detector that detects an ambient temperature of the steering mechanism, wherein the steering angle calculation unit corrects the rotation angle detected by the motor angle detector or the shaft angle detector on the basis of the ambient temperature detected by the temperature detector and uses the corrected rotation angle to calculate the steering angle.
