An image forming apparatus, comprising: an image bearing member on which an electrostatic image is to be formed; a developing device (5a, 5b, 5c, 5d) including a developer container for containing a developer, a developer carrying member for developing the electrostatic image with the developer carried thereon, and a contact portion which is contactable to said image bearing member; a movable member for rotationally moving said developing device mounted therein toward a position in which said developing devices opposes said image bearing member, said movable member including: a rotation shaft member, a first member which is engaged with the rotation shaft member with play at one end portion of the rotation shaft member with respect to a rotational axis direction of the rotation shaft member, a second member which is engaged with the rotation shaft member with play at the other end portion of the rotation shaft member with respect to the rotational axis direction, a first guide portion which is provided in the first member and with which a first portion to be guided (9a11) which is provided at one end of said developing device is engageable with play, and a second guide portion which is provided in the second member and with which a second portion to be guided (9e11) which is provided at the other end of said developing device is engageable with play; a first swingable supporting member for rotatably supporting said movable member at the one end portion of the rotation shaft member in said movable member and for swingably supporting said movable member relative to a main assembly of said image forming apparatus; a second swingable supporting member for rotatably supporting said movable member at the other end portion of the rotation shaft member in said movable member and for swingably supporting said movable member relative to the main assembly; an urging portion (108, 109) for urging said movable member toward said image bearing member; a first preventing portion for preventing movement of the first member in the rotational axis direction; and a second preventing portion for preventing movement of the second member in the rotational axis direction. an image bearing member on which an electrostatic image is to be formed; a developing device (5a, 5b, 5c, 5d) including a developer container for containing a developer, a developer carrying member for developing the electrostatic image with the developer carried thereon, and a contact portion which is contactable to said image bearing member; a movable member for rotationally moving said developing device mounted therein toward a position in which said developing devices opposes said image bearing member, said movable member including: a rotation shaft member, a first member which is engaged with the rotation shaft member with play at one end portion of the rotation shaft member with respect to a rotational axis direction of the rotation shaft member, a second member which is engaged with the rotation shaft member with play at the other end portion of the rotation shaft member with respect to the rotational axis direction, a first guide portion which is provided in the first member and with which a first portion to be guided (9a11) which is provided at one end of said developing device is engageable with play, and a second guide portion which is provided in the second member and with which a second portion to be guided (9e11) which is provided at the other end of said developing device is engageable with play; a first swingable supporting member for rotatably supporting said movable member at the one end portion of the rotation shaft member in said movable member and for swingably supporting said movable member relative to a main assembly of said image forming apparatus; a second swingable supporting member for rotatably supporting said movable member at the other end portion of the rotation shaft member in said movable member and for swingably supporting said movable member relative to the main assembly; an urging portion (108, 109) for urging said movable member toward said image bearing member; a first preventing portion for preventing movement of the first member in the rotational axis direction; and a second preventing portion for preventing movement of the second member in the rotational axis direction.