An image forming apparatus of the present invention includes a charging device including a charge roller formed with annular grooves at opposite end portions thereof and configured to charge an image carrier. Annular gap forming members each are fitted in the annular grooves for forming a gap between the charge roller and the image carrier. The gap forming members each have an area of 1.010^-6 m² to 3.010^-6 m² in a section containing the axis of the charge roller.