Lt Col Nikorn Chuthong and a team of officers from Tha Chat Chai and Sakoo arrested the man, Samkhan Pongwut, 35, at a check point set up in Sakoo.
Affter stopping Samkhan at the check point, police checked under the seat of his motorcycle and found a Spanish-made Llama 7.65mm pistol, 18 bullets, a holster and two magazines.
Samkhan was charged with possession of a gun and ammunition without a permit and with carrying a gun illegally in a public place.