An image forming apparatus includes an accommodating container provided at one end thereof with a toner supply port, a stirring conveying member that conveys toner to the supply port, a rotational driving unit that rotationally drives the stirring conveying member, a current detection unit that detects a driving current, an overload detection section that detects that the stirring conveying member is in an overload state when the driving current is within a range of an excess current, an unevenness determination section that determines whether the toner has been unevenly accumulated at the one end or the other end of the accommodating container, and a cause determination section that determines that a cause of the overload is uneven distribution of the toner when the overload state of the stirring conveying member is detected and being determined that the toner has been unevenly accumulated at the one end or the other end.