Looks like a model 99 Arisaka 7.7mm. The following is from
WW2 Jap Weapons. swords, grenades, pistols, MGs
The Arisaka was named after the Colonel who oversaw its adoption in 1897. The 38th Year designation referred to the uniquely Imperial Japanese practice of basing a calendar on the length of time a particular Emperor had ruled. When the original model was amended in 1905, the Emperor Meiji had been on the throne for thirty eight years.
The Arisaka was a reliable and popular weapon in the East, its low recoil 6.5 mm round being appreciated for its ease of handling. It was, however, also its greatest weakness. The 6.5 mm round was known to be less effective than the 7.62 mm or higher rounds used elsewhere, especially by Japan's foes. A revised model, the Type 99 was produced in 1939. It fired the 7.7 mm round used in the Japanese heavy machine gun. It supplemented the earlier version in service, but production was too limited to replace it. Its statistics were roughly similar to the Type 38 given above.
Both models came in a shortened carbine form, the Type 38 at around 87 cm in length and 3.3 kg in weight, while the Type 99 was 112 cm and 3.9 kg. Ammunition was carried in two pouches, each holding a half dozen five rounds clips for a total of sixty rounds for the average soldier.