Irvin Fraser of Aberdeen pleaded guilty in Sheriff's Court, The Scotsman reported.
Fraser, who has two real children, started small in 2003, claiming benefit for two additional imaginary children. By late 2005, his fictional family had 14 children.
In 2006, when he was questioned by investigators for Revenue and Customs, Fraser was using four different names and collecting benefits for 36 children.
Sheriff Alexander Jessup said he was surprised to discover that someone could get additional benefits by making a telephone call to report another child.
"The children didn't even exist -- don't you need a birth certificate or something?" he asked.
Annette Fraser, Fraser's partner, has pleaded not guilty in the scheme.
Shane Campbell, Fraser's lawyer, said that his client was spending from $300 to $400 a day on heroin when he started cheating.