The purpose of the present invention is to ascertain film characteristics with high precision using a simpler method. A method for manufacturing film (1) using a film-manufacturing process monitor device (100), comprising: a spectrum acquisition step for radiating wideband light (L1), which is near-infrared light, from a light source (10) toward the film (1) moved in direction A to thereby receive diffused reflected light (L2) emitted from a film (1) in a light-receiving unit (30) and thereby acquire a spectrum of the diffused reflected light (L2) in a spectrum acquisition unit (40a) of an analyzer (40); and a physical value calculation step for calculating physical values related to the film (1) from the acquired spectrum of the differed reflected light (L2). Since physical values indicating the characteristics of the film (1) can be obtained by acquiring a spectrum, the characteristics of a film can be ascertained in a simple manner, and, e.g., a plurality of pieces of information can be acquired from the spectrum. Therefore, the characteristics of a film can be ascertained with higher precision.