Police patrols have now been stepped up after the incident outside Victoria Shopping Centre this morning, Friday. The man was taken to hospital with injuries to his face, back and leg. Police were called at 4.40am.
The boys, aged 13, 16 and 15, were arrested on Skipton Road at around 5.20am. They all remain in police custody.
The victim, a local man in his 30s, was taken to hospital with serious but not life-threatening injuries.
Superintendent Steve Thomas, Harrogate Commander, said: "This is clearly an extremely serious incident, and residents will naturally feel concerned about what has happened. However, incidents like this are very rare in our town. Thanks to a fast response by local officers last night, three suspects have been arrested, and a police investigation is well underway.
"You can expect to see increased patrols in the town centre in the coming days - officers from the Neighbourhood Policing Team will be in the area to provide extra reassurance to residents and businesses.
"Please do speak to them if you have any concerns. It goes without saying that the carrying of knives and other weapons is unacceptable and these additional patrols will be using appropriate stop and search powers to ensure anyone found in possession of weapons is arrested and put before the courts."
Anyone with any information about the incident or anyone who witnessed the attack should contact North Yorkshire Police on 101, quoting reference 12200001239.