PURPOSE: To eliminate a measured distance error due to thermal deformation of a laser range finder setting frame by constantly enabling zero point correction of a laser range finder by way of providing a correction surface for the laser range finder only immediately below the laser range finder on the lower surface side of a carrier table.

CONSTITUTION: A rolled steel plate is carried by a roll 1. A tandem type calibrater 12 used for zero point correction of a laser range finder 3 has its part immediately below the laser range finder 3 which is a protruded shape, and the upper surface of the protruded part corresponding to a laser irradiation surface is machined flat and smooth. A part except for the laser irradiation surface is of a recessed shape and an auxiliary roller for transportation is built in it. A laser beam of the laser range finder 3 arranged with a constant pitch orthogonal in the transport direction constantly emits, and in the case when there is no steel plate immediately below it, it is irradiated on the upper surface of the protruded part of the calibrater 12, which calibrates a distance between the laser range finder 3 and the calibrater protruded part so that a position of the protruded part upper surface becomes a zero point by way of detecting the reflected laser beam. Consequently, a distance measurement error caused by deformation due to steel plate radiation heat of a frame installing the laser range finder 3 on it is calibrated to be constantly zero.