Investigators say Dmitry Vinogradov also wounded another twopeople at the pharmaceutical firm where he worked.
The 30-year-old is now in police custody.
He had reportedly been drinking for five days and had declaredhis hatred for humankind in an online posting.
"The suspect came into the office... and fired numerous shotsfrom Saiga and Benelli shotguns that he owns," Russianinvestigators were quoted as saying in a statement by the AFP newsagency.
"As a result, three men and two young women sitting at theirdesks died on the spot. One more man and another young woman werewounded," the statement added.
The suspect - who was dressed in camouflage gear - is believedto have fired shots from the two guns simultaneously.
Reports say that the woman he was in love with was injured inthe shooting.
Mr Vinogradov had posted on one of Russia's most popular socialnetworks before the shooting, Russia's news agencies say.
"I hate human society and being part of it disgusts me! I hatethe meaningless of human life!" Mr Vinogradov is believed to havewritten.
"I hate the life itself. I see only one way to justify it: toeliminate as many particles of human compost as possible."
He is now being questioned by the police, and reports say hewill undergo a psychological evaluation.