A developing blade 10 is insert molded by forming a rib portion 13 which projects from an end portion in the longitudinal direction of a blade body 12 in the transverse direction of the blade body 12, opposite to the contact surface 12a side of the blade body 12, on the blade body 12 in contact with the developing roll of the developing blade 10 and forming the gate 21G of a metal mold 20 in which a metal plate 11 as an insert member has been installed only in a cavity 21b corresponding to the above rib portion 13. Therefore, a developing blade 10 without burrs and recesses on its contact surface with the developing roll or without welds can be easily manufactured.