The man entered the famous landmark shortly after 1:00 pm local time and advanced towards the private security guard, threatening him for around eight minutes with a knife, according to Italian news agency ANSA.
After the arrival of nearby officers on patrol and a brief mediation, the man dropped the knife and was arrested.
Milan’s Deputy Mayor Anna Scavuzzo said in a statement the man had entered the cathedral in order to evade a police check.
Police said they were trying to determine the man’s identity.
The man has been charged with kidnapping, resisting arrest and the illegal possession of a knife.
With ANSA