a developing apparatus includes a roller - shaped developer carrying member , a frame for holding the developer carrying member , and a magnetic seal member for preventing leakage of a developer from an end of the developer carrying member in a longitudinal direction of the developer carrying member . the magnetic seal member includes an arcuate magnet portion to be disposed along a circumferential direction of the developer carrying member , and a non - arcuate portion which extends from an end , in the circumferential direction , of the magnet portion away from a peripheral surface of the developer carrying member and is different in material from the magnet portion .