Authors: TheIndianSubcontinent News Agency
The video was released online on Tuesday. Militant websites affiliated with the Islamic State group posted it.
The video shows two hostages the militants identify as Kenji Goto Jogo and Haruna Yukawa.
But the Japanese government said it would not bow to extremism.
"Our country's stance - contributing to the fight against terrorism without giving in - remains unchanged," chief government spokesman Yoshihide Suga told a news conference in Tokyo.
An official in the foreign ministry's terrorism prevention division had said earlier that the government was investigating the threat.