During an operation, a control device (38) for performing output control of an engine (10) determines whether or not the engine (10) and/or an exhaust gas purifying device (18) has a malfunction. If it is determined that the engine (10) and/or the exhaust gas purifying device (18) has a malfunction, a highest rotational speed of the engine (10) is controlled to a second rotational speed (Nt) higher by a predetermined amount (α) than a first rotational speed (Ns) at which an engine maximum torque (Tm) before the malfunction can be outputted. In this case, a maximum fuel injection quantity of the engine (10) is limited so that a rated torque (Tr) before the malfunction can be outputted at the first rotational speed (Ns).