1. A manufacturing method of an organic EL element in which film depositions of a plurality of layers are gradually executed in a plurality of film forming chambers, comprising: a step of measuring a film thickness of a film deposition product by using an optical film thickness measuring apparatus installed outside each film forming chamber; and a step of feeding the film deposition product to the film forming chamber installed in a next stage, if the film thickness measured by the optical film thickness measuring apparatus achieves a preset film thickness.