A Queens subway rider made a gruesome discovery on the tracks Wednesday morning — the decapitated body of a man who cops said had deliberately wanted to be beheaded by a train.

The straphanger spotted the remains on the track while waiting for an F train at about 8:50 a.m. at the 169th Street station in Jamaica, and alerted a station agent.

The agent in turn alerted the rail-control center, which notified the motorman of the next train entering the station.

The medical examiner told police that it appears the victim had placed his head on the tracks in a way to let a train decapitate him as it entered the station. No criminality is suspected in the apparent suicide.

Police had a tentative name for the man, believed to be 50 years old, but had not tracked down relatives.The Manhattan-bound F train bypassed the station until noon.