An image forming apparatus comprising: a main housing; a drive unit including a drive output shaft configured to generate a rotational drive force for axial rotation; an image bearing member disposed in the main housing and having a peripheral surface for bearing a toner image; a developing unit attached to the main housing to be detachable by pulling out, the developing unit including a developing roller having a peripheral surface for carrying toner thereon and configured to supply the toner to the image bearing member, and a first drive input section configured to supply a rotational drive force to the developing roller; a support unit supported by the main housing to be freely pivotable about an axis of a pivot shaft, the supporting unit being configured to place and support the developing unit in position; an urging member configured to generate an urging force for urging the support unit to pivot in one of pivoting directions about the pivot shaft, the one pivoting direction coinciding with an approaching direction for moving the peripheral surface of the developing roller toward the peripheral surface of the image bearing member; and a switching mechanism configured to switch the support unit supporting the developing unit, the switching being made between a first position in which the peripheral surface of the developing roller is located relatively close to the peripheral surface of the image bearing member and a second position in which the peripheral surface of the developing roller is located relatively away from the peripheral surface of the image bearing member, wherein the support unit includes a second drive input section disposed coaxially with the pivot shaft and configured to receive a rotational drive force from the drive output shaft, and a transmission mechanism configured to transmit the rotational drive force received by the second drive input section to the first drive input section, and the rotational drive force generated by the drive output shaft is for rotation in a direction of pivoting the support unit in the approaching direction. a main housing; a drive unit including a drive output shaft configured to generate a rotational drive force for axial rotation; an image bearing member disposed in the main housing and having a peripheral surface for bearing a toner image; a developing unit attached to the main housing to be detachable by pulling out, the developing unit including a developing roller having a peripheral surface for carrying toner thereon and configured to supply the toner to the image bearing member, and a first drive input section configured to supply a rotational drive force to the developing roller; a developing roller having a peripheral surface for carrying toner thereon and configured to supply the toner to the image bearing member, and a first drive input section configured to supply a rotational drive force to the developing roller; a support unit supported by the main housing to be freely pivotable about an axis of a pivot shaft, the supporting unit being configured to place and support the developing unit in position; an urging member configured to generate an urging force for urging the support unit to pivot in one of pivoting directions about the pivot shaft, the one pivoting direction coinciding with an approaching direction for moving the peripheral surface of the developing roller toward the peripheral surface of the image bearing member; and a switching mechanism configured to switch the support unit supporting the developing unit, the switching being made between a first position in which the peripheral surface of the developing roller is located relatively close to the peripheral surface of the image bearing member and a second position in which the peripheral surface of the developing roller is located relatively away from the peripheral surface of the image bearing member, wherein the support unit includes a second drive input section disposed coaxially with the pivot shaft and configured to receive a rotational drive force from the drive output shaft, and a transmission mechanism configured to transmit the rotational drive force received by the second drive input section to the first drive input section, and a second drive input section disposed coaxially with the pivot shaft and configured to receive a rotational drive force from the drive output shaft, and a transmission mechanism configured to transmit the rotational drive force received by the second drive input section to the first drive input section, and the rotational drive force generated by the drive output shaft is for rotation in a direction of pivoting the support unit in the approaching direction.