A combustion control device for an internal combustion engine, comprising: a combustion pressure sensor including a pressure receiving member that is inserted into a hole leading to a combustion chamber of the internal combustion engine with a vacant space left between the pressure receiving member and the hole, and outputting a signal corresponding to displacement of the pressure receiving member, in response to the pressure receiving member being displaced in accordance with a pressure in the combustion chamber; a crank angle sensor that outputs a signal synchronized with rotation of a crankshaft of the internal combustion engine; and an arithmetic processing device that receives a signal from the combustion pressure sensor and a signal from the crank angle sensor, and performs arithmetic operation for controlling a combustion state in the combustion chamber, wherein the arithmetic processing device is configured to execute first processing of calculating a heat generation amount that is a value obtained by totaling a heat amount generated in the combustion chamber from a start of combustion of one combustion cycle for each crank angle in the combustion cycle based on the signal from the combustion pressure sensor and the signal from the crank angle sensor, and thereby generating heat generation amount data in which the heat generation amount and the crank angle are related to each other, second processing of calculating an estimated heat generation amount that is estimated from a fuel amount, based on the fuel amount supplied to the combustion chamber in the combustion cycle, characterized in that the arithmetic processing device is further configured to execute third processing of calculating a combustion state parameter expressing a combustion state in the combustion chamber, based on the heat generation amount data from a start of combustion to a crank angle corresponding to a final value of the heat generation amount in the combustion cycle, when the final value is equal to or smaller than the estimated heat generation amount, and fourth processing of calculating the combustion state parameter, based on the heat generation amount data from the start of combustion to a crank angle at which the heat generation amount reaches the estimated heat generation amount, when the final value in the combustion cycle is larger than the estimated heat generation amount. a combustion pressure sensor including a pressure receiving member that is inserted into a hole leading to a combustion chamber of the internal combustion engine with a vacant space left between the pressure receiving member and the hole, and outputting a signal corresponding to displacement of the pressure receiving member, in response to the pressure receiving member being displaced in accordance with a pressure in the combustion chamber; a crank angle sensor that outputs a signal synchronized with rotation of a crankshaft of the internal combustion engine; and an arithmetic processing device that receives a signal from the combustion pressure sensor and a signal from the crank angle sensor, and performs arithmetic operation for controlling a combustion state in the combustion chamber, wherein the arithmetic processing device is configured to execute first processing of calculating a heat generation amount that is a value obtained by totaling a heat amount generated in the combustion chamber from a start of combustion of one combustion cycle for each crank angle in the combustion cycle based on the signal from the combustion pressure sensor and the signal from the crank angle sensor, and thereby generating heat generation amount data in which the heat generation amount and the crank angle are related to each other, second processing of calculating an estimated heat generation amount that is estimated from a fuel amount, based on the fuel amount supplied to the combustion chamber in the combustion cycle, characterized in that the arithmetic processing device is further configured to execute third processing of calculating a combustion state parameter expressing a combustion state in the combustion chamber, based on the heat generation amount data from a start of combustion to a crank angle corresponding to a final value of the heat generation amount in the combustion cycle, when the final value is equal to or smaller than the estimated heat generation amount, and fourth processing of calculating the combustion state parameter, based on the heat generation amount data from the start of combustion to a crank angle at which the heat generation amount reaches the estimated heat generation amount, when the final value in the combustion cycle is larger than the estimated heat generation amount.