A diesel engine system includes a diesel engine, a throttle valve, an EGR (Exhaust Gas Recirculation) path, an EGR valve and a controller. The throttle valve controls a flow rate of intake air to the diesel engine. Exhaust gas is recirculated along the EGR path from an exhaust port to an intake port of the diesel engine. The EGR valve controls a flow rate of the exhaust gas. The controller controls the throttle valve and the EGR valve such that an opening of the throttle valve decreases and an opening of the EGR valve increases when a load of the diesel engine increases. The controller controls the EGR valve such that the opening of the EGR valve increases after the opening of the EGR valve is held constant for a first predetermined holding time.