The invention provides a blow-by gas recirculating apparatus for a crankcase with enhanced ventilation efficiency. A fresh air introducing chamber is remote from a head cover. An upstream intake passage of a throttle valve is communicated with the fresh air introducing chamber, and the fresh air introducing chamber is communicated with a crankcase through a crankcase communication throttle hole which is opened in the crankcase. Fresh air in the upstream intake passage of the throttle valve is introduced into the crankcase sequentially through a fresh air introducing passage, the fresh air introducing chamber, and the throttle hole, without being short-circuited to a PCV valve. In a reverse flow from the crankcase to the upstream intake passage of the throttle valve, a gas in the crankcase reversely flows into the upstream intake passage sequentially through the throttle hole, the fresh air introducing chamber, and the fresh air introducing passage.