Pol Col Panya Karawanant, the Sai Buri police chief, said the killing occurred about 10.10am.
Anuchart Kongkaew was posted at Lalo intersection in tambon Rahan. His attackers arrived in a pick-up truck and opened fire at him with war weapons, then fled.
Anuchart was hit many times in the body. He was admitted to Sai Buri hospital where he was pronounced dead.
Police recovered at least 10 spent bullet cases at the scene.