To provide a method of manufacturing a glow plug which allows two kinds of components selected from among a main fitting, a heater, and an outer cylinder member to be efficiently and surely pressed and fitted together.

A support 20 is used to fixedly support the main fitting 5 in such a manner as to control the axial movement of the main fitting, and a sheath heater 2 is inserted into the main fitting 5. Thereafter, the tip of the sheath heater 2 is made to abut on the lower end face (in the figure) of an ultrasonic generator 60 comprising a first component part 61 which produces ultrasonic vibration and a second component part 62 which amplifies the amplitude of the ultrasonic vibration, and a first pressing member 63 is made to abut on the upper end face (in the figure) of the ultrasonic generator. Also, a continuous load is applied to the first pressing member 63 whereby the main fitting 5 and the sheath heater 2 are pressed and fitted together.