1. An obstacle detection apparatus comprising: a main body which can be moved along a surface of the ground; a movement amount determination module which determines whether an amount of movement of the main body is outside a predefined threshold range; a posture determination module which determines a changed posture of the main body with respect to the surface of the ground according to the amount of movement of the main body; and a state determination module which determines a state of an obstacle according to the results of the determination performed by the movement amount determination module or according to the results of the determination performed by the posture determination module.