A fixing device for fixing a toner image printed on a recording medium having a specific heat capacity, the fixing device comprising: a rotatable fuser member being an endless belt and subjected to heating; a heater configured to heat the fuser member to a heating temperature (Theat); a rotatable pressure member disposed opposite the fuser member; a fixing nip which is formed by the fuser member and the pressure member which are pressed against each other to form the fixing nip therebetween, through which the recording medium is conveyed with a first, printed surface thereof facing the fuser member and a second, non-printed surface thereof facing the pressure member, so as to fix the toner image in place under heat and pressure as the fuser and pressure members (2, 3) rotate together; a thermometer disposed adjacent to the pressure member and configured to detect an operational temperature (Tpress) of the pressure member; and a feedback controller operatively connected with the thermometer; characterized by: a memory configured to store a lookup table, which associates a specific operational temperature (Tpress) of the pressure member with an optimal heating temperature (Theat) for maintaining a post-fixing temperature (Tpf) at a setpoint temperature (Tset), the memory being connected to the feedback controller, wherein the feedback controller is configured to control the heating temperature (Theat) according to the detected operational temperature (Tpress) by means of the lookup table, so that the recording medium exhibits the substantially constant post-fixing temperature (Tpf) downstream from the fixing nip regardless of the heat capacity of the recording medium; wherein the controller is configured to adjust the heating temperature (Theat) based on an operational parameter with which the recording medium in use is processed through the fixing nip; wherein the operational parameter includes a composite parameter obtained by combining at least two of nip dwell time, basis weight, thermal conductivity, specific heat capacity, and moisture content of the recording medium in use. a rotatable fuser member being an endless belt and subjected to heating; a heater configured to heat the fuser member to a heating temperature (Theat); a rotatable pressure member disposed opposite the fuser member; a fixing nip which is formed by the fuser member and the pressure member which are pressed against each other to form the fixing nip therebetween, through which the recording medium is conveyed with a first, printed surface thereof facing the fuser member and a second, non-printed surface thereof facing the pressure member, so as to fix the toner image in place under heat and pressure as the fuser and pressure members (2, 3) rotate together; a thermometer disposed adjacent to the pressure member and configured to detect an operational temperature (Tpress) of the pressure member; and a feedback controller operatively connected with the thermometer; a memory configured to store a lookup table, which associates a specific operational temperature (Tpress) of the pressure member with an optimal heating temperature (Theat) for maintaining a post-fixing temperature (Tpf) at a setpoint temperature (Tset), the memory being connected to the feedback controller, wherein the feedback controller is configured to control the heating temperature (Theat) according to the detected operational temperature (Tpress) by means of the lookup table, so that the recording medium exhibits the substantially constant post-fixing temperature (Tpf) downstream from the fixing nip regardless of the heat capacity of the recording medium; wherein the controller is configured to adjust the heating temperature (Theat) based on an operational parameter with which the recording medium in use is processed through the fixing nip; wherein the operational parameter includes a composite parameter obtained by combining at least two of nip dwell time, basis weight, thermal conductivity, specific heat capacity, and moisture content of the recording medium in use.