Control device of an internal combustion engine that determines whether or not to perform sensor element heating control of an air-fuel ratio sensor with high accuracy based on the mass of condensed water in an exhaust pipe. The control device computes the rate of change of condensed water mass in an exhaust pipe based on the saturated water vapor pressure and the water vapor partial pressure of exhaust gas, and computes the rate of change of evaporation mass in the exhaust pipe based on the amount of heat which the condensed water receives in the exhaust pipe. The control device updates the mass of condensed water based on the rate of change of condensed water mass and the rate of change of evaporation mass, and determines whether or not to perform heating control by a heating controlling unit based on the updated mass of condensed water.