A driver state estimation device 1 includes a steering angle sensor 2 detecting a steering angle of a steering, a steering torque sensor 3 detecting steering torque applied to the steering, and an ECU 4 having a steering angle estimation unit 5 and a driver state estimation unit 6. The steering angle estimation unit 5 is input with a steering angle (steering angle detected value) MA detected by the steering angle sensor 2 and steering torque (steering torque detected value) MT detected by the steering torque sensor 3, determines whether the steering angle detected value MA is 0 or not, when the steering angle detected value MA is 0, calculates a steering angle estimated value MAest by multiplying the steering torque detected value MT by the gradient of the steering angle (proportionality coefficient) α with respect to the steering torque, and when the steering angle detected value MA is not 0, sets the steering angle detected value MA as the steering angle estimated value MAest.