He's just released a hostage.
The man, saying he was linked to al-Qaeda, demanded to speak to the elite Raid police unit that shot Islamist gunman Mohamed Merah.
Merah, who claimed al-Qaeda training, killed seven people in Toulouse before he was shot dead by police in March.
There are no reports of injuries in the incident so far.
The man went into the branch of the CIC bank at 10:10 local time (08:10 GMT), taking the manager and three other people hostage, French media say.
The area around the bank has been cordoned off and two nearby schools have been closed.