A fuel injection system in the present invention is provided with a fuel injection valve (10) which incorporates a heater (20) for heating fuel before being injected. The temperature of the heater (20) is estimated on the basis of the resistance value RHtr of the heater (20). The temperature of the heater (20) estimated at or after the time of occurrence of a point of inflection in the resistance value RHtr of the heater (20) is corrected in order to reduce to zero the difference between the nucleate boiling start point temperature and the estimated temperature value of the heater (20) at the time of occurrence of the point of inflection.