The arrests were made on Sunday after the gang was said to have stolen the tourist’s gold necklace before throwing him into a canal, news portal Thaiger reported.
A relative of the victim’s girlfriend posted the incident on social media, prompting local police to investigate.
The suspects admitted to assaulting the Swedish man but denied stealing his gold necklace. They said their alleged harassment of the waitress was "just a joke." Police said they are collecting evidence to make charges against the suspects.
Thailand received 11 million foreign visitors last year, and eyes 30 million this year.