James Potter walked up to Steven Collins as he sat in his car with the evening’s takings and pointed an imitation handgun at his face.
He told Mr Collins, 24: “I’ll be taking that. Do you think this is no real?”
The High Court in Edinburgh heard that the delivery driver formed the impression that he was faced with a real firearm.
Advocate depute Alex Prentice QC said that Mr Collins was concerned for his safety and that of his girlfriend who was with him and handed over £175.
Unemployed Potter, 27, then told his victim: “That’s not it all.”
But Mr Collins showed him that other items he was holding were receipts and Potter headed off.
The victim’s partner called police who were given a description of the robber following the incident in High Street, Prestonpans, in East Lothian.
Mr Prentice said police traced Potter shortly afterwards and he was seen to throw something into the garden of a house.
Potter was detained and the discarded item was recovered and found to be the £175 proceeds of the robbery.
The fake firearm was discovered to be a child’s cap gun.
Potter, who has previous convictions including assault and possession of an offensive weapon, admitted assaulting and robbing Mr Collins on October 11 last year by presenting an imitation handgun at him while on bail.
The court heard that Mr Collins worked as a part-time delivery driver for a Chinese takeaway restaurant in Prestonpans.
On the night of the robbery Potter had earlier approached his car which his girlfriend was sitting in and asked her for a lighter which he returned.
After he had made several deliveries Mr Collins had returned to the High Street and was getting ready to cash up for the night when Potter struck.
The judge, Lady Wolffe, deferred sentence on Potter, who was described as a prisoner in Edinburgh, for the preparation of a background report.