To easily set each of output levels of plural optical sensors at a proper level in a microfilm retrieving device discriminating the existence of a frame from a change in the output of an optical sensor detecting a received light quantity by arranging the end faces of many pairs of optical fibers so as to be opposed by holding film in between and receiving light led to the film from one optical fiber by the other paired optical fiber.

This device is provided with a level adjusting until 112 separately adjusting the output level of each pair of the optical sensors, a level discriminating part 114 discriminating whether or not the output level, adjusted by the level adjusting unit 112 in a state where microfilm 26 does not exist between the end faces of each pair of the optical fibers 104 and 106 or in the state where microfilm density is set at a fixed value, is within a specified set level range and a display unit 116 displayed the discriminated result of the level discriminating part 114. The level discriminating part 114 is formed of a window comparator discriminating a target set level range. The level discriminating part 114 and the display unit 116 are separately provided for each pair of the optical fibers 104 and 106, so that it is convenient to simultaneously confirm the display unit 116 of each pair.