A film formation method is used for forming a silicon nitride film on a target substrate by repeating a plasma cycle and a non-plasma cycle a plurality of times, in a process field configured to be selectively supplied with a first process gas containing a silane family gas and a second process gas containing a nitriding gas and communicating with an exciting mechanism for exciting the second process gas to be supplied. The method includes obtaining a relation formula or relation table that represents relationship of a cycle mixture manner of the plasma cycle and the non-plasma cycle relative to a film quality factor of the silicon nitride film; determining a specific manner of the cycle mixture manner based on a target value of the film quality factor with reference to the relation formula or relation table; and arranging the film formation process in accordance with the specific manner.