Two men armed with guns made their way into the restaurant shortly after 10pm.
They then tied up the maître d’, who was alone at the time because the restaurant was closed.
According to the Göteborgs-Posten (GP) newspaper, the thieves made off with 50,000 kronor ($7,200) in cash.
About ten minutes after the robbers fled, the maître d’ managed to untie himself and call the police.
“Currently we don’t have any suspects. We’re looking for more witnesses and are hoping for help from the public,” police spokesperson Thomas Alm told the TT news agency.
Sjömagasinet, one of Sweden’s most famous restaurants, holds a one-star rating in the Guide Michelin.
Restaurateur Leif Mannerström, Sjömagasinet’s owner, told GP that the restaurant rarely has much cash on hand since most customers pay by credit or debit card.
He also lamented that one of his most trusted employees had been a victim in the robbery.
“The man who was robbed is one of my most experienced maître d’s. According to what I’ve heard, the robbers threatened to shoot him in the leg. It doesn’t feel so pleasant,” Mannerström told GP.