To activate a substrate, while suppressing deformation or cracking of the substrate, when rapidly heating the substrate using a flash lamp for ion implantation or activation on a top surface.

In a substrate heating device which heats a substrate by radiating light from a flush lamp, a semiconductor switch 25 is connected in series to the flush lamp 5. Then, a trigger electrode 52 of the flash lamp 5 is input with trigger signal, and after that, a first drive signal and second drive signal are output from a gate circuit 28. Thus, the time period, during which a semiconductor switch 25 is kept on by the second drive signal, becomes longer than the time period during which the semiconductor switch 25 is kept on by one drive signal among the first drive signals. The semiconductor switch is turned on/off by the first drive signal so that the temperature of the substrate is raised to a temperature which lower than the desired target value, and its condition is kept for a short period. Then, the surface temperature of the substrate is raised to the desired target value.