In order to provide an ignition control device 30 which can efficiently control timing of thermal ignition of gaseous mixture in a combustion region 10, the peak estimation part 32, the ignition timing determination part 33, the control timing determination part 34, and the plasma control part 35 control timing of thermal ignition of the gaseous mixture in the combustion region 10 by controlling the pulse generator 36, the electromagnetic wave oscillator 37, the mixer circuit 38, and the spark plug 15 so as to increase the amount of OH radicals in the combustion region 10 during a low-temperature oxidation preparation period that occurs prior to a peak of a heat release rate before the thermal ignition of the gaseous mixture.