A fixing device comprising: an endless belt; a heater that is disposed to be in contact with an inner surface of the belt; a pressing member that is positioned to face the heater with the belt interposed therebetween and configured to press a conveyed sheet against the belt and the heater; wherein the heater is divided into a plurality of heater blocks (41- 44) in a width direction of the belt; the fixing device further comprising: a plurality of temperature sensors (56, 57, 58, 153) that are disposed respectively in each of at least half of the heater blocks; and a processor configured to select one or more heater blocks on the basis of a width of the conveyed sheet to form a heat generation block, and control electric power supplied to said one or more heater blocks so that a temperature of the heat generation block is within a predetermined temperature range, characterized in that the processor is further to configured to select the temperature sensor of the plurality of temperature sensors that is disposed in a heater block of the plurality of heater blocks having a non-paper passing region and control an excessive temperature rise in the non-paper passing region based on a temperature detected by the selected temperature sensor. an endless belt; a heater that is disposed to be in contact with an inner surface of the belt; a pressing member that is positioned to face the heater with the belt interposed therebetween and configured to press a conveyed sheet against the belt and the heater; wherein the heater is divided into a plurality of heater blocks (41- 44) in a width direction of the belt; the fixing device further comprising: a plurality of temperature sensors (56, 57, 58, 153) that are disposed respectively in each of at least half of the heater blocks; and a processor configured to select one or more heater blocks on the basis of a width of the conveyed sheet to form a heat generation block, and control electric power supplied to said one or more heater blocks so that a temperature of the heat generation block is within a predetermined temperature range, characterized in that the processor is further to configured to select the temperature sensor of the plurality of temperature sensors that is disposed in a heater block of the plurality of heater blocks having a non-paper passing region and control an excessive temperature rise in the non-paper passing region based on a temperature detected by the selected temperature sensor. a plurality of temperature sensors (56, 57, 58, 153) that are disposed respectively in each of at least half of the heater blocks; and a processor configured to select one or more heater blocks on the basis of a width of the conveyed sheet to form a heat generation block, and control electric power supplied to said one or more heater blocks so that a temperature of the heat generation block is within a predetermined temperature range, characterized in that the processor is further to configured to select the temperature sensor of the plurality of temperature sensors that is disposed in a heater block of the plurality of heater blocks having a non-paper passing region and control an excessive temperature rise in the non-paper passing region based on a temperature detected by the selected temperature sensor. select one or more heater blocks on the basis of a width of the conveyed sheet to form a heat generation block, and control electric power supplied to said one or more heater blocks so that a temperature of the heat generation block is within a predetermined temperature range, characterized in that the processor is further to configured to select the temperature sensor of the plurality of temperature sensors that is disposed in a heater block of the plurality of heater blocks having a non-paper passing region and control an excessive temperature rise in the non-paper passing region based on a temperature detected by the selected temperature sensor.