A moving body attitude angle processing apparatus capable of reducing cumulative errors in continuously measuring the attitude angle of a moving body is provided. The moving body attitude angle processing apparatus estimates the attitude angle of a moving body in accordance with outputs from an acceleration sensor, a magnetic sensor, and a gyro sensor that are mounted to the moving body, and outputs the attitude angle thus estimated. The moving body attitude angle processing apparatus includes: a gyro sensor that outputs an angular velocity vector; an acceleration sensor that outputs an acceleration vector; a magnetic sensor that outputs a magnetic field vector; a movement state determining device that determines a movement state of a moving body in accordance with an output from the acceleration sensor; and a gyro-sensor zero-point output estimating device that, when the movement state determining device determines the movement state to have been detected as a stationary state of the moving body, carries out a process of estimating a zero-point output of the gyro sensor in accordance with the output from the acceleration sensor, an output from the magnetic sensor, and an output from the gyro sensor.