Kathu Police were called to the scene, an apartment building in Soi Pho Hid, in Moo 6, Kathu, at 5pm.
The injured man, identified as Natchapon Srangmuang, was found conscious but with a gunshot wound to his left rib cage, just below his breast.
After receiving initial first aid, Mr Natchapon was taken to Vachira Phuket Hospital.
Mr Natchapol’s girlfriend, who lives in the apartment with him, told police that she was folding clothes in the room when she heard a loud bang.
At first she thought it was the sound of a hair dryer exploding, but then turned around and saw Mr Natchapon wounded. He was cleaning his handgun when it accidentally fired, she said.
Police confiscated as evidence the illegally made handgun and four shotgun cartridges found in the room.
Other evidence, including tests for gunpowder residue from both Mr Natchapon and his girlfriend, were collected. Drug tests were also conducted on Mr Natchapon as part of the investigation, police noted.
Police have since detained Mr Natchapon for further questioning and potential legal action, pending the results of the investigation, police said.