Police were called to the scene at approximately 10.40pm on Wednesday, November 4, after two men forced staff to open the safe and proceeded to take the cash.
The men, aged 24 and 25, were armed with a gun and a knife and have since been apprehended and released on bail.
Acting Sergeant Kenny Brogan said: "This was a terrifying ordeal for the member of staff and they must be praised for their bravery.
"Armed robberies like this are rare in Bristol but when they do happen we always carry out a thorough investigation and move quickly to bring those responsible to justice.
"While we have arrested two men in connection with this incident, our enquiries are continuing and I'd ask anyone with information to please get in touch using the 24-hour enquiry line 101 quoting reference number 5215034037.