The man, who went into Coral in Queens Road at around 8pm on Thursday, left in the direction on Hanson Lane.
Nobody was injured during the incident.
Police today appealed for information on the robbery.
Detective Constable Will Burgess, of Calderdale CID, said: “I would appeal to anyone who was around the Queens Road area on Thursday evening and may have seen or heard anything suspicious to come forward.
“Fortunately, no one was injured during the incident, but clearly this has been a frightening experience for those working in the bookmakers at the time. Enquiries are ongoing.”
Anyone with information is asked to contact DC Burgess at Calderdale CID via 101, quoting 13160290899.