Devi Singh, 45, was posted at Dariyavganj police outpost. He is survived by three children.
According to reports, the sub-inspector's body was recovered from the building's staircase along with his service revolver, nine bullets and one 9 mm cartridge fired from the weapon.
The body was sent for post-mortem.
Kasganj SP Sushil Ghule said that the exact reason behind the suicide was yet to be ascertained.
"Our internal initial probe suggests that the deceased sub-inspector had no excessive workload. Before committing suicide, he came on his motor-bike at the under-construction fire brigade building at around 4.30 p.m. where he was spotted by the watchman. The two interacted for a while and the SI left the premises. One hour later, he returned back to the building and shot himself while the guard was out of the premises," the SP said.
The cop had a clean record in his service, he added.
The incident is an addition to the growing list of suicides by cops in Uttar Pradesh.
Arjun Rana, attached with Bijnore police lines allegedly shot himself with his service rifle on August 16.
Another constable Madhup Singh, posted at Balni police station in Baghpat committed suicide at his residence in Ghaziabad on the same day.
In May, head-constable Sanjeev Balyan, posted at Nagfani police station in Moradabad, had shot himself while on duty. Earlier in March, a 24-year-old UP Police constable, Arun Kumar, had committed suicide by hanging himself from a tree in Mathura.
Kuldeep Singh, a sub-inspector from Kankarkheda area in Meerut, committed suicide at his residence in Deoband area in January.
( With inputs from IANS )