PURPOSE: To reduce a consumption power and to perform a display suitable for a compact, light and portable type, by a method wherein a matrix-shaped display element is enbaled to display measurements such that one coordinate corresponds to a length of an optical fiber and the other coordinate to an amount of reflected light.

CONSTITUTION: Comparing circuits 2-1W2-10, equivalent to the number of semiconductor luminous elements in an ordinate direction, are located at an output of an ordinate circuit 5, the voltage produced in en ordinate is divided into 10 equal parts, and threshold voltages V1WV10 corresponding to the original voltage are inputted to the comparing circuits 2-1W2-10, respectively. Out of contents of a memory storing an amount of reflected light, 12 contents are selected at given intervals in a direction of a lengh of an optical fiber, the 12 memory contents are repeatedly read by means of a sampling pulse with a specified period to add them to the ordinate circuit 5, and original sampling pulses are added, in order, to terminals H1WH12. An AND circuit 4 is located to an intersecting point of the output of the comparing circuit and a matrix of a terminal in a abscissa and the output is connected to a semiconductor element 1. This causes emitting of semiconductor luminous elements 1 of which a matrix in 10×12 consists.