The Romanian diners, who had paid a deposit of â‚¬900 ($950; Â£770), left the El Carmen restaurant in Bembibre as dessert was due to be served, Antonio Rodriguez said.
"It happened in the space of a minute," he said. "It was something they had planned and they left in a stampede."
The diners owe â‚¬2,000 more, he said.
Mr Rodriguez gave police the details on the reservation but said he held out little hope of being repaid. Police told El Pais newspaper they had not yet been able to contact any of the diners.
The diners had consumed starters, a main course and 30 bottles of various alcoholic drinks, he said, adding that it was the first time in 35 years of working in the restaurant trade that he had seen seen anything comparable.
Some 120 diners celebrating a baptism at a restaurant in a north-western Spanish town all fled the restaurant at once without paying, the owner said.