An internal EGR amount calculation device for an internal combustion engine, which is capable of properly and easily calculating an internal EGR amount according to the change in the valve timing and enhancing the calculation accuracy of the internal EGR amount. The device includes an ECU. The ECU calculates an amount of burned gases remaining in a cylinder when the valve timing is predetermined reference timing, as a reference internal EGR amount. The ECU calculates a change in the amount of burned gases flowing into or out of the cylinder with respect to the amount of burned gases flowing into or out of the cylinder when the valve timing is the predetermined reference timing, as an internal EGR increase/decrease amount. Then, the ECU calculates the internal EGR amount by adding the internal EGR increase/decrease amount to the reference internal EGR amount.