The man got off the train at the Alterlaa stop, then realized that something was missing - the baby carriage with his young baby, according to a report from the Austrian news daily Österreich.
By the time he realized it, the train had already started to leave the station.
In a panic, he immediately contacted the Wiener Linien hotline. The service, which gets around 2,000 calls every day, responded professionally despite the unusual nature of the complaint.
Most people call about leaving an umbrella or bag on board, but this case demanded a lot more action. The caller said "Help, I forgot my baby in the subway."
The metro authorities immediately ordered a halt of all trains in the stations, and station personnel conducted a thorough search.
Fortunately, the baby carriage was found in short order, and the child - who was still sleeping calmly in his pram - was reunited with his father.
Wiener Linien employee Ralf Hartwig Hochfilzer-Schützenhöfer said: "When the man called me and said he had forgotten his baby in the subway, I could not at first believe it. He was very excited and for a short time, didn't even know which subway line he was travelling on."