an internal combustion engine , wherein a hydrocarbon supply valve and an exhaust gas purification catalyst are disposed inside an engine exhaust gas passage . when an increase in the temperature of the exhaust gas purification catalyst caused by hydrocarbons supplied from the hydrocarbon supply valve is smaller than a predetermined increase amount , and a decrease in the pressure of fuel supplied to the hydrocarbon supply valve when the hydrocarbons have been injected from the hydrocarbon supply valve is larger than a predetermined decrease amount , the present invention determines that a blockage is occurring in a hydrocarbon injection channel when the hydrocarbons have been injected from the hydrocarbon supply valve .