A developing device includes a rotatable developer carrying member, first and second chambers configured to accommodate developer supplied to the developer carrying member, and first and second rotatable feeding members provided in the first and second chambers, respectively. A first communication port permits feeding of the developer from the second chamber to the first chamber, and a second communication port permits feeding of the developer from the first chamber to the second chamber. In addition, a toner content detecting portion includes a planar detecting surface including at least a planar coil generating a magnetic field and detects the toner content. The detecting surface is provided in the first communication port above a bottom of the first communication port and is disposed substantially in a central portion of the first communication port.