To provide a heating device that quickly raises a temperature of a matter to be heated such as resin materials and moreover, prevents the occurrence of failure due to overheating of the matter to be heated.

In order to retain the temperature of the resin materials at a temperature higher than a first temperature SV, heater drive circuits 35, 36, 37 are controlled such that temperatures of a first heater 9, a second heater 10 and a third heater 11 alternately repeat the rise and drop between the first temperature SV and a second temperature SV+dSV(n) set by adding a temperature increase dSV(n) to the first temperature SV.