A control apparatus, a control method, and an engine control unit for a variable cylinder internal combustion engine are provided for appropriately performing any of an idling rotational speed control, a deceleration fuel-cut control, and an auxiliary machinery driving control irrespective of whether or not a cylinder pausing mechanism fails. The control apparatus for the variable cylinder internal combustion engine switchably operated in a full cylinder operation mode and a partial cylinder operation mode comprises an ECU. The ECU determines whether or not the cylinder pause mechanism fails,and sets a target idling rotational speed for use in the idling rotational speed control to a normal operation value when the cylinder pausing mechanism is normal and to a faulty operation value higherthan the normal operation value when the cylinder pausing mechanism is faulty.