According to an embodiment, a device includes processing circuitry. The processing circuitry performs three-dimensional measurement of surroundings of a mobile object to obtain a three-dimensional point group. The processing circuitry calculates movement information. The processing circuitry makes a threshold value based on time series differences in the movement information. The processing circuitry extracts, from the three-dimensional group, three-dimensional points having distance to the mobile object in a moving direction of the mobile object to be equal to or smaller than the threshold value. The processing circuitry divides space, in which the three-dimensional points are present, into divided spaces in the moving direction. The processing circuitry selects a representative point for the divided space from among three-dimensional points included in the divided space. The processing circuitry estimates, as a surface for motion on which the mobile object moves, a surface which approximates the representative points.