Glow plug tip temperature estimating method and glow plug drive control device

It is an object of the present invention to make the temperature of a glow plug tip extremely simply and precisely estimable. An arithmetic and control unit 23 is configured to arithmetically calculate a resistance value of a glow plug 1 on the basis of an energization current of the glow plug 1 and a voltage applied to the glow plug 1 (S104), perform a multiplication of the resistance value and a constant that has been determined beforehand on the basis of an electrical characteristic of the glow plug 1, input a predetermined heater reference point temperature (S106), calculate an offset with a predetermined offset arithmetic expression from the heater reference point temperature (S108), correct the multiplication result with that offset, and take the correction result as an estimated temperature of a tip of the glow plug 1.