A fuel cut during deceleration is executed at time point t1. An oxygen storage amount (rOS) which increases with this fuel cut is estimated based on an exhaust air-fuel ratio and an intake air quantity. When the oxygen storage amount (rOS) reaches a threshold value (at time point t2), a target compression ratio (tCR) is corrected to become lower than a basic target compression ratio (tCR). Although a fuel recovery is executed at time point t4, a combustion temperature is lowered because of the lowering of the mechanical compression ratio, so that a production of NOx in a combustion chamber is suppressed. Therefore, worsening of NOx is suppressed even if the oxygen storage amount (rOS) of exhaust-emission purification catalyst (4) is excessive.