PURPOSE: To execute development suitable for thermal dissociation capsule toner and to obtain excellent printing quality and developer having long life by using jamping developing system.

CONSTITUTION: The thermal dissociation capsule toner being magnetic toner containing magnetic powder is used in this developing method in which a photosensitive body 1 holding an electrostatic latent image on its surface and a non-magnetic sleeve 3 carrying the magnetic toner on its surface and having a magnet inside are faced so as to hold a gap equal to or above the thickness of a magnetic toner layer in a developing part, they are turned in the same direction, and electric field in the developing gap is alternated both in an image part and a non-image part, then development is performed while giving alternating electric field whose frequency is ≤1kHz.