A determination method of non-destructively and easily determining a state of an aggregate of a plurality of cells formed by three-dimensional culture is provided. A determination method according to the disclosed technology includes generating a phase difference image of an aggregate of a plurality of cells from a hologram obtained by imaging the aggregate, deriving a phase difference amount density by dividing a total phase difference amount that is a value obtained by integrating a phase difference amount of each of a plurality of pixels constituting the phase difference image by a volume of the aggregate, and determining a state of the aggregate on the basis of a time transition of the phase difference amount density.