The man was transported to Ulleval University Hospital in Oslo by an air ambulance and was listed in serious condition, Norwegian broadcaster NRK reported.
The shot was fired by a hunter about 100 yards from the cottage on Vesteroy island, police said.
NRK said the victim's wife wasn't holding a grudge against the hunter who accidentally shot her husband.
Police Chief Anders Saether said he suspected the hunter didn't really notice his surroundings before shooting.
Police said it was too soon to know whether any action would be taken against the hunter.