An electrophotographic image forming apparatus comprising: a process cartridge including a casing; an electrophotographic photosensitive drum having an axis and being rotatably supported in the casing to permit rotation about the axis; and a coupling member (150; 1350; 1450; 1550; 1750; 1850; 3150; 5150; 6150; 7150; 8150; 9150; 9250; 9350; 9450; 10150; 11150; 12150; 12250; 12350; 13150; 14150; 15150; 16150; 17150; 20150; 21150) having an axis, the coupling member having (i) a rotational force transmitting portion (150h; 1550h; 5150h; 8150g; 9150h; 14150h; 15150b, 15150h), (ii) a rotational force receiving portion (150e; 1550e; 3150a; 5150e; 6150e; 7150e; 8150a, 8150e; 9150e; 12350e; 14150e; 15150a, 15150e), and (iii) a connecting portion (7150c; 14150c; 15150c) that connects the rotational force receiving portion to the rotational force transmitting portion, the electrophotographic image forming apparatus further comprising: a main assembly including a driving motor; a driving shaft engageable with the rotational force receiving portion of the coupling member of the process cartridge and having a rotational axis; a guide portion (130R1, 130R2, 130L1, 130L2; 1130R1, 1130R2) configured to guide insertion of the process cartridge into the image forming apparatus along a direction that is substantially perpendicular to the rotational axis of the driving shaft; and an urging member movable between an urging position and a retracted position retracted from the urging position, characterized in that the electrophotographic photosensitive drum has a flange (151; 15151) at one end thereof that is coaxial with the axis, the rotational force transmitting portion of the coupling member is engageable with the flange and movable between a first position in which the axis of the coupling member is coaxial with the axis of the electrophotographic photosensitive drum, and a second position in which the axis of the coupling member is inclined with respect to the axis of the electrophotographic photosensitive drum, wherein the image forming apparatus is configured such that, during the process of mounting the process cartridge to the image forming apparatus, the coupling member is inclined toward the driving shaft by being urged by an elastic force of the urging member restoring to the urging position after being temporarily retracted to the retracted position by being contacted by the coupling member. a casing; an electrophotographic photosensitive drum having an axis and being rotatably supported in the casing to permit rotation about the axis; and a coupling member (150; 1350; 1450; 1550; 1750; 1850; 3150; 5150; 6150; 7150; 8150; 9150; 9250; 9350; 9450; 10150; 11150; 12150; 12250; 12350; 13150; 14150; 15150; 16150; 17150; 20150; 21150) having an axis, the coupling member having (i) a rotational force transmitting portion (150h; 1550h; 5150h; 8150g; 9150h; 14150h; 15150b, 15150h), (ii) a rotational force receiving portion (150e; 1550e; 3150a; 5150e; 6150e; 7150e; 8150a, 8150e; 9150e; 12350e; 14150e; 15150a, 15150e), and (iii) a connecting portion (7150c; 14150c; 15150c) that connects the rotational force receiving portion to the rotational force transmitting portion, (i) a rotational force transmitting portion (150h; 1550h; 5150h; 8150g; 9150h; 14150h; 15150b, 15150h), (ii) a rotational force receiving portion (150e; 1550e; 3150a; 5150e; 6150e; 7150e; 8150a, 8150e; 9150e; 12350e; 14150e; 15150a, 15150e), and (iii) a connecting portion (7150c; 14150c; 15150c) that connects the rotational force receiving portion to the rotational force transmitting portion, a main assembly including a driving motor; a driving shaft engageable with the rotational force receiving portion of the coupling member of the process cartridge and having a rotational axis; a guide portion (130R1, 130R2, 130L1, 130L2; 1130R1, 1130R2) configured to guide insertion of the process cartridge into the image forming apparatus along a direction that is substantially perpendicular to the rotational axis of the driving shaft; and an urging member movable between an urging position and a retracted position retracted from the urging position, a driving motor; a driving shaft engageable with the rotational force receiving portion of the coupling member of the process cartridge and having a rotational axis; a guide portion (130R1, 130R2, 130L1, 130L2; 1130R1, 1130R2) configured to guide insertion of the process cartridge into the image forming apparatus along a direction that is substantially perpendicular to the rotational axis of the driving shaft; and an urging member movable between an urging position and a retracted position retracted from the urging position,