A change in geoid height is measured easily. A geoid measurement method of the present invention executes an inertial measurement data acquiring step, a comparison data acquiring step, a state variable estimating step, and a geoid calculating step. In the inertial measurement data acquiring step, data related to velocity, position, and attitude angle is acquired as inertially-derived data based on the output of an inertial measurement part having a three-axis gyro and a three-axis accelerometer attached to a moving body. In the comparison data acquiring step, data related to velocity is acquired as comparison data from a source other than the inertial measurement part. In the state variable estimating step, state variables including a plumb line deviation are estimated by using the inertially-derived data and the comparison data to apply a Kalman filter in which the plumb line deviation is included in the state variables.