A controlling method of an inkjet printer wherein the_inkjet printer comprising a printing part for applying ink to a medium before printing, a drying drum for heating and drying a medium after printing (la) having the ink applied in contact with an outer circumstantial face of the drying drum,_controller capable of individually controlling heating of a plurality of sections obtained by dividing the drying drum along a plane perpendicular to a shaft direction of the drying drum,_and guide rolls guiding the medium, the medium is an elongated medium, each of the sections is mounted with a heater part capable of heating the corresponding section, and heating of the heater parts of all of the sections is continuously controlled individually by the controller, the heating parts can heat the sections according to output ratios which are percentages of output capacities of the sections; each of the sections is further mounted with a temperature detecting part for detecting a temperature of the corresponding section individually; the controller has an initial output ratio setting part for setting an initial output ratio, a target temperature setting part for setting target temperatures of the plurality of sections, a storage part for storing an output increase/decrease operation expression and an output limitation operation expression, and an operation part for computing the output ratios sequentially based upon the output increase/decrease operation expression and the output limitation operation expression; the output increase/decrease operation expression is used to obtain an additional output ratio by multiplying by a coefficient set freely a temperature difference obtained by subtracting one of actually measured temperatures detected by the temperature detecting parts of the sections from an average temperature of the actually measured temperatures, and to add the additional output ratio to the initial output ratio of the corresponding section; the output limitation operation expression is used to adopt the output ratio having the additional output ratio added based upon the output increase/decrease operation expression as an updated output ratio if the output ratio is 100% or less, and to adopt the output ratio of 100% as an updated output ratio if the output ratio exceeds 100%; and by the controller, heating starts of the heater parts of the respective sections are controlled with the initial output ratio set freely, and heating of the heater parts of the respective sections after the heating starts is continuously controlled with the updated output ratio. the_inkjet printer comprising a printing part for applying ink to a medium before printing, a drying drum for heating and drying a medium after printing (la) having the ink applied in contact with an outer circumstantial face of the drying drum,_controller capable of individually controlling heating of a plurality of sections obtained by dividing the drying drum along a plane perpendicular to a shaft direction of the drying drum,_and guide rolls guiding the medium, the medium is an elongated medium, each of the sections is mounted with a heater part capable of heating the corresponding section, and heating of the heater parts of all of the sections is continuously controlled individually by the controller, the heating parts can heat the sections according to output ratios which are percentages of output capacities of the sections; each of the sections is further mounted with a temperature detecting part for detecting a temperature of the corresponding section individually; the controller has an initial output ratio setting part for setting an initial output ratio, a target temperature setting part for setting target temperatures of the plurality of sections, a storage part for storing an output increase/decrease operation expression and an output limitation operation expression, and an operation part for computing the output ratios sequentially based upon the output increase/decrease operation expression and the output limitation operation expression; the output increase/decrease operation expression is used to obtain an additional output ratio by multiplying by a coefficient set freely a temperature difference obtained by subtracting one of actually measured temperatures detected by the temperature detecting parts of the sections from an average temperature of the actually measured temperatures, and to add the additional output ratio to the initial output ratio of the corresponding section; the output limitation operation expression is used to adopt the output ratio having the additional output ratio added based upon the output increase/decrease operation expression as an updated output ratio if the output ratio is 100% or less, and to adopt the output ratio of 100% as an updated output ratio if the output ratio exceeds 100%; and by the controller, heating starts of the heater parts of the respective sections are controlled with the initial output ratio set freely, and heating of the heater parts of the respective sections after the heating starts is continuously controlled with the updated output ratio.