A breather apparatus for an internal combustion engine for a vehicle, comprising: an air cleaner disposed above a crankcase which forms part of an engine main body incorporated in a vehicle body frame and supports a crankshaft for rotation; characterized in that the breather apparatus further comprises: a breather tube coupled with a breather chamber formed in the air cleaner and configured to guide blow-by gas exhausted from the crankcase, wherein an upstream side flow path with which the breather tube is coupled and a downstream side flow path continuously extending from the upstream side flow path in a substantially U shape are provided in the breather chamber; wherein the breather chamber is formed from a bottom plate which forms the bottom portion of the air cleaner, a wall portion provided in a projecting manner from the bottom plate so as to continuously extend in an endless (ring-shaped) form so as to form an outer wall of the breather chamber, and a lid member fixed to a projecting end of the wall portion, a cutout communicating with a purification chamber in the air cleaner is provided on at least one of the lid member and a portion of the wall portion near to the lid member, a passage member (43F, 43R) for guiding air to the engine main body side is disposed so as to extend through the bottom plate such that an upstream end portion of the passage member (43F, 43R) communicates with the purification chamber, and a slit (52, 53) communicating with a lower portion in the air cleaner is formed on a side wall of the passage member (43F, 43R). an air cleaner disposed above a crankcase which forms part of an engine main body incorporated in a vehicle body frame and supports a crankshaft for rotation; characterized in that the breather apparatus further comprises: a breather tube coupled with a breather chamber formed in the air cleaner and configured to guide blow-by gas exhausted from the crankcase, wherein an upstream side flow path with which the breather tube is coupled and a downstream side flow path continuously extending from the upstream side flow path in a substantially U shape are provided in the breather chamber; wherein the breather chamber is formed from a bottom plate which forms the bottom portion of the air cleaner, a wall portion provided in a projecting manner from the bottom plate so as to continuously extend in an endless (ring-shaped) form so as to form an outer wall of the breather chamber, and a lid member fixed to a projecting end of the wall portion, a cutout communicating with a purification chamber in the air cleaner is provided on at least one of the lid member and a portion of the wall portion near to the lid member, a passage member (43F, 43R) for guiding air to the engine main body side is disposed so as to extend through the bottom plate such that an upstream end portion of the passage member (43F, 43R) communicates with the purification chamber, and a slit (52, 53) communicating with a lower portion in the air cleaner is formed on a side wall of the passage member (43F, 43R). a breather tube coupled with a breather chamber formed in the air cleaner and configured to guide blow-by gas exhausted from the crankcase, wherein an upstream side flow path with which the breather tube is coupled and a downstream side flow path continuously extending from the upstream side flow path in a substantially U shape are provided in the breather chamber; wherein the breather chamber is formed from a bottom plate which forms the bottom portion of the air cleaner, a wall portion provided in a projecting manner from the bottom plate so as to continuously extend in an endless (ring-shaped) form so as to form an outer wall of the breather chamber, and a lid member fixed to a projecting end of the wall portion, a cutout communicating with a purification chamber in the air cleaner is provided on at least one of the lid member and a portion of the wall portion near to the lid member, a passage member (43F, 43R) for guiding air to the engine main body side is disposed so as to extend through the bottom plate such that an upstream end portion of the passage member (43F, 43R) communicates with the purification chamber, and a slit (52, 53) communicating with a lower portion in the air cleaner is formed on a side wall of the passage member (43F, 43R).