The following is performed when controlling the convergent beam irradiation of laser beams by using a spatial light modulator: obtaining the laser beam wavelength number, each wavelength value, and the laser beam incidence conditions (Step S101); setting the convergent beam points, the convergent beam position at each convergent beam point, the wavelength, and the convergence strength (S104); deriving a distorted phase pattern to be imparted to the laser beams at each convergent beam point by an optical system containing a spatial light modulator (S107); and considering the distorted phase pattern, and designing a modulation pattern to be provided to the spatial light modulator (S108). In addition, designing the modulation pattern involves using a design method focusing on the phase value effect of one pixel, and using a propagation function to which the distorted phase pattern has been added when evaluating the convergent beam state at the convergent beam points. As a result, it is possible to achieve: a light modulation control method capable of favorably controlling laser beam convergence; a program; a device; and a laser beam irradiation device.