A developing device for an image forming apparatus includes both a layer height restricting blade for controlling a thickness of the developer layer on a developer supply roller, and a spike-height restricting blade. The spike-height restricting blade is located downstream from the layer height restricting blade, and upstream from the position at which an electrostatic latent image bearing member and the developer supply roller are closest to each other. Preferably, the tip of the spike-height restricting blade is located downstream from a radial line along which a main magnetic pole of the device projects half of its maximum magnetic field strength.