To provide a light-shielding method which is indispensable to the measurement of modules, will not cause leakage of light having different sizes, even if the sizes of the modules, which are transferred and are measured, are diverse, and to provide a device for this light-shielding method.

A light-shielding means 4, formed in such a way as to be able to automatically vary the size of apertures 3c, is arranged between a solar cell module Bm to be measured and a light source 3b for test, the size of the module Bm, which is transferred on the facing surface of the light source 3b, is measured beforehand on this side of the light source 3b and on the basis of data on the size which is found by this measurement, of the module Bm or on the basis of data on the size, which was separately measured previously of the module Bm, the size of apertures 4a formed in the means 4 is changed to in conformity with the size of the module Bm.