A first arrival flow rate that is a flow rate of evaporative fuel gas that has arrived in a throttle downstream portion located downstream of a throttle valve in an intake pipe via a second purge passage after passing through a purge control valve is estimated based on a valve passage flow rate that is a flow rate of evaporative fuel gas that has passed through the purge control valve, and a first response delay in the flow of evaporative fuel gas through a route extending from the purge control valve to the throttle downstream portion via the second purge passage.