Detectives are linking the incident in Cleckheaton with a second robbery in nearby Gomersal, during which a van driver was attacked.
The first incident happened between noon and 12.15pm as the security man walked into a bank on Albion Street.
He was approached by two men who assaulted him, stole the money and fled the scene in a dark blue Mini with black alloy wheels, which was waiting outside the building.
The victim suffered minor injuries during the incident.
Shortly afterwards a man who was putting up signs on the road in Gomersal was assaulted.
The suspects stole his van, which is described as a white Renault panel van, while it was parked up in Burnley Mills Road at around 12.50pm.
They left the scene in the direction of Spen Lane.
Police said the victim suffered minor injuries but was left distressed by the incident.
Detective Inspector Mark Walker, of Kirklees District CID, said: “We believe these two robberies are linked and are appealing to members of the public to come forward if they were in the area of either of these incidents to help us with our enquiries.
“Both victims in these incidents thankfully suffered minor injuries, but have been left distressed by their ordeals.
The first suspect is described as a stocky, white man, and was around 5ft 6in.
The second man was described as white, skinny and around 5ft.
Det Insp Walker said: “I would like to speak to anyone who was in the area, saw anyone behaving suspiciously, or saw either of the vehicles to come forward and contact the police.”
Anyone with any information is asked to contact Kirklees CID via 101 quoting reference 13160511074 or alternatively contact independent charity Crimestoppers anonymously on 0800 555 111.