A developing apparatus includes a developing roller and a sealing member. The developing roller applies toner to an electrostatic latent image to develop the electrostatic latent image. The sealing member presses the developing roller to seal the developer. The apparatus includes a developing roller with a shaft and a resilient layer formed on the shaft. The developing roller rotates about the shaft. The resilient layer covers the outer circumferential surface of the developing roller and is in contact with the sealing member. The resilient layer has a diameter that becomes larger nearer longitudinal ends of the developing roller. The diameter has a maximum value and a minimum value. The difference between the maximum value and the minimum value is such that 10 .mu.m<.DELTA..PHI.<300 .mu.m, where .DELTA..PHI. is a difference between the maximum value and the minimum value.