Joel Reed used a crowbar and screwdriver to smash his way into a rear office within Monarch Coin Laundry on Mill Road, Cambridge, on 24 March.
He ransacked the room looking for cash and made off with just £15 but as he was leaving the shop, two members of the public entered, and he pointed a knife at them.
The pair ran out of the store, as another member of the public arrived, and hid around the corner to call police.
They then watched Reed make off on a bike.
Reed was arrested at his home in Cromwell Road, Cambridge after being identified on CCTV.
Shoes that he was wearing upon his arrest also matched footprints at the scene.
At Peterborough Crown Court on Thursday, Reed, 30, was sentenced to three years in prison after previously pleading guilty to aggravated burglary and possession of a blade in a public place.
Detective Constable Timothy Taylor, who investigated, said: “Reed went to the laundry armed with a knife and used it to point it at the people who came inside.
“Any crime involving possession of knives are treated extremely seriously and we welcome this prison sentence.”
If you know someone who is carrying a knife, report it to us online www.cambs.police.uk/report
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