A data processing device processes measurement data measured by a sensor that measures three-dimensional coordinates of a measurement object from a first position and a second position which are different. The data processing device includes a controller. The controller acquires measurement data of three or more planes of the measurement object from the sensor, the planes having different normal vectors. The controller finds, from the acquired measurement data, a transformation expression that integrates a coordinate system of the sensor at the second position into a coordinate system of the sensor at the first position.