PURPOSE: To reduce the cost by providing a detecting means detecting the position of a point in the circumferential part of a rail head and providing a moving means for letting the detecting means reciprocate by crossing the rail head when moving along the rail.

CONSTITUTION: When a rail trolley is actuated along the length direction of a rail 20, a carriage 16 and a detector 18 are reciprocated by crossing the rail 20 by an eccentric actuation mechanism. A detecting wheel 80 of a detector 18 detects the position of a point in the circumferential part of the rail head 24 in such a state as energized by the rail heat 24 by an air spring 86 via a detecting bracket 74. Data obtained by the detecting wheel 80 are sent to a computer to be computed so that the profile of the rail head 24 is decided.