PURPOSE: To make adjustable a part for measuring the luminous intensity of a surface even when an object is cured, by a construction wherein the shape of arrangement of the end faces of the respective optical fiber wires of an optical fiber array disposed on the image plane of a first lens can be matched with an arbitrary line.

CONSTITUTION: The titled device is constructed so that the shape of arrangement of the end faces of the respective optical fiber wires of an optical fiber array 3 disposed on the image plane of a first lens 2 can be altered arbitrarily. When a continuous casting line of ironworks is cured, for instance, each holder 8 into which the end portion of each optical fiber wire of the optical fiber array 3 and which is supported by a guide 9 is moved arbitrarily in the direction of the length thereof, so that the shape of arrangement of the respective end faces of the fiber wires can be so adjusted as to correspond to the shape of the casting line. Lights entering a second lens 4 from the other end faces of the optical fiber array 3 are converted into electric signals by a sensor array 5 and sent therefrom to a signal processing circuit 6.