Developing device

A developing device comprising:

• a developing roller being cylindrical in shape, housing a magnetic-field generating member, and rotating;
• a regulation member including a first opposing surface facing an outer circumferential surface of the developing roller;
• a magnetic member arranged on an upstream side surface of the regulation member with respect to a rotating direction of the developing roller;
• and
• a synthetic resin member arranged on an upstream side surface of the magnetic member with respect to the rotating direction of the developing roller, wherein
• the regulation member regulates a layer thickness of magnetic toner on the outer circumferential surface of the developing roller using the first opposing surface,
• the synthetic resin member includes a second opposing surface facing the outer circumferential surface of the developing roller,
• the second opposing surface is tilted at 40° or more but 60° or less with respect to the first opposing surface to be increasingly distant from the outer circumferential surface of the developing roller toward an upstream side in the rotating direction of the developing roller,
• a solubility parameter of a material of the synthetic resin member is 23 (J/cm3)1/2 or more, and
• the magnetic toner contains toner and resin fine particles.