a temperature control system for a hot nozzle is used in a runner - less molding process of a plastic by an injection molding machine . the control system includes first and second temperature detecting devices for detecting the temperature of the hot nozzle at the front end of the hot nozzle and at a position upstream of the front end , respectively . control signal outputting units compare the temperature detected by the first and second temperature detecting devices with a first set temperature and a second set temperature , respectively . based on the temperature differences , first and second control signals corresponding to the temperature differences are calculated and are outputted from the control signal outputting units to a power supply unit which is connected to a power source for regulating the power for heating the hot nozzle . a switch is connected between the control signal outputting units and the power supply unit and is operable to selectively supply either one of the first and second temperature control signals to the power supply unit according to the molding cycle .