In a process cartridge having a latent-image-bearing member and a developing device having a developer-holding part and a developing member, at a vertical section which bisects in the process cartridge the surface of the latent-image-bearing member with which surface the developing member is brought into pressure contact, a developer agitation and transport member has at least two rotary agitation and transport members having rotating shafts falling at right angles with the vertical section. Where, at the vertical section, the area of the developer-holding part is represented by S1 and the area of the part corresponding to the movable region of the rotary agitation and transport member is represented by S2, the ratio of S2 to S1, S2/S1, is from 0.8 to 0.99; and the ratio of a long side Sa to a short side Sb, Sa/Sb, of a circumparallelogram having a minimum area in respect to the area S1 in the vertical section is from 1.5 to 3.0. The non-magnetic one-component developer contains at least a binder resin and a colorant and has a fluidity index of from 50 to 90 and a floodability index of from 45 to 96.