To provide a method for accelerating the growth of short day plants and neutral plants by utilizing a light supplement in short time at nights.

This method for accelerating growth is provided by irradiating far-infrared light at the beginning of the nights for the short day plants and neutral plants. Here, as for the supplement of light by the light, it is sufficient to secure a light energy amount (irradiance × time length) in an extent of inducing the growth acceleration reaction, and even with a weak light for a short time, it is possible to cause the induction.