Provided is an engine which is provided with an EGR device, wherein: an actual intake/exhaust gas pressure ratio π1 of an intake-gas pressure P1 to an exhaust-gas pressure P2 is calculated from the detected exhaust-gas pressure P2 and the detected intake-gas pressure P1; an estimated intake/exhaust gas pressure ratio π2 of the intake-gas pressure P1 to the exhaust-gas pressure P2 is calculated from an engine rotational frequency N, and a fuel injection amount F; and, in cases when the actual intake/exhaust gas pressure ratio π1 is less than a prescribed value π0, an EGR gas weight Megr is calculated based on the actual intake/exhaust gas pressure ratio π1, and in cases when the actual intake/exhaust gas pressure ratio π1 is equal to or more than the prescribed value π0, the EGR gas weight Megr is calculated based on the estimated intake/exhaust gas pressure ratio π2.