This engine system is provided with a throttle device (14), an EGR valve (18), and an ECU (50). The ECU (50) diagnoses an abnormality of the EGR valve (18) on the basis of an operating state during an engine deceleration, and diagnoses combustion deterioration of an engine (1) on the basis of a crank angle speed change during the engine deceleration (not during a fuel cut-off). The ECU (50) executes an engine stall avoidance control with the throttle device (14) when it is determined there is an abnormality in the EGR valve (18), makes a final determination that the EGR valve (18) has an abnormality and continues the engine stall avoidance control when it is determined thereafter that there is combustion deterioration, and makes a final determination that the EGR valve (18) is normal and releases the engine stall avoidance control when it is determined that there is no combustion deterioration.