PURPOSE: To provide the effective cylinder heating devices of an extruding machine and an injection molding machine at relatively low cost by inserting cartridge heaters or sheath heaters into a plurality of longitudinal through holes arranged in between the beginning end and the finishing end of a cylinder wall at an equal distance in a peripheral direction.

CONSTITUTION: When sheath heaters 5' are inserted into longitudinal through holes 2, if the wound pitches at the central part and both end parts of the heating element in the sheath heater 5', are arranged sparsely or densely so as to uniformalize the calorific value in the longitudinal direction of the sheath heater 5', the temperature at the front and rear parts of a cylinder 1 are suitably uniformalized. If the brim edge part 4 into which the sheath heater 5' is inserted, is divided into two parts of front and rear, and one sheath heater is respectively inserted into each part, the temperature is effectively uniformalized.