Provided is a film-forming method based on an LB method by which a uniform alignment film using a helical polyacetylene can be obtained. The method based on the LB method includes: developing a helical polyacetylene onto a liquid surface; and transferring a monolayer film of the helical polyacetylene formed on the liquid surface onto a substrate to form a film, in which a compressibility P represented by the following formula (1) at a time of the film formation is 1×10−2 m/mN or less: P=(1/(dH/dS))×(1/S) (1), where H represents a surface pressure (mN/m) of the monolayer film of the helical polyacetylene, and S represents an area (m2) of the monolayer film of the helical polyacetylene developed onto the liquid surface.