Patent ID: 8192339

Claim:
A developing roller on a circumferential surface of which toner is held, comprising: a plurality of first grooves formed in parallel to each other at approximately equal intervals, each in a direction inclined to a circumferential direction of the circumferential surface of the developing roller; a plurality of second grooves formed in parallel to each other at approximately equal intervals, each in a direction inclined to the circumferential direction of the circumferential surface of the developing roller, each second groove intersecting each first groove, the first groove and the second groove each having a U-shaped cross section; and a protrusion portion disposed in an area surrounded by the first groove and the second groove, wherein the first groove and the second groove are configured to contain the toner and roll the toner to the protrusion portion to put the toner into contact with the circumferential surface, wherein: the protrusion portion has on a top surface thereof a plurality of minute projections; a surface roughness Rz of the top surface is R O and R O is 0.5 to 2 times an average grain size of a particle of the toner; a distance from an average line of a roughness curve of the surface roughness R O to a deepest part of the first groove is D 1 and a distance from the average line of the roughness curve of the surface roughness R O to a deepest part of the second groove is D 2 , each of D 1 and D 2 is 0.5 to 2 times the average grain size of the particle of the toner; and a relationship of the R O <D 1 and the R O <D 2 is satisfied.