A transfer device comprising: an endless belt image bearer which is rotatably stretched around a plurality of stretching members (10, 11, 12, 13); a driving roller configured to drivingly rotate the belt image bearer, the driving roller being one of the plurality of stretching members (10, 11, 12, 13); a first driving motor configured to drivingly rotate the driving roller; a first speed detecting unit configured to detect a rotational speed of the belt image bearer; a rotatable transfer member configured to abut an outer peripheral surface of the belt image bearer and form a transfer nip, wherein an image borne on the outer peripheral surface of the belt image bearer is transferred onto a transfer material that is sandwiched in the transfer nip; a second driving motor configured to drivingly rotate the transfer member; a second speed detecting unit configured to detect a rotational speed of the transfer member; a contact separation unit configured to cause the belt image bearer and the transfer member to separate from each other in a first state, and cause the belt image bearer and the transfer member to contact each other in a second state; and characterized by a relative speed setting unit configured to acquire a first value relating to a driving torque of the first driving motor and a second value relating to a driving torque of the second driving motor in the first state, and acquire a third value relating to the driving torque of the first driving motor and a fourth value relating to the driving torque of the second driving motor in the second state, calculate a variation amount, the variation amount being an amount of variation of the third value and the fourth value with respect to the first value and the second value, and obtain and set a relative speed of the belt image bearer and the transfer member, such that the calculated variation amount is less than a predetermined variation amount; and a control unit configured to control the first driving motor and the second driving motor such that the belt image bearer and the transfer member are rotated at rotational speeds corresponding to the relative speed set by the relative speed setting unit in the second state. an endless belt image bearer which is rotatably stretched around a plurality of stretching members (10, 11, 12, 13); a driving roller configured to drivingly rotate the belt image bearer, the driving roller being one of the plurality of stretching members (10, 11, 12, 13); a first driving motor configured to drivingly rotate the driving roller; a first speed detecting unit configured to detect a rotational speed of the belt image bearer; a rotatable transfer member configured to abut an outer peripheral surface of the belt image bearer and form a transfer nip, wherein an image borne on the outer peripheral surface of the belt image bearer is transferred onto a transfer material that is sandwiched in the transfer nip; a second driving motor configured to drivingly rotate the transfer member; a second speed detecting unit configured to detect a rotational speed of the transfer member; a contact separation unit configured to cause the belt image bearer and the transfer member to separate from each other in a first state, and cause the belt image bearer and the transfer member to contact each other in a second state; and characterized by a relative speed setting unit configured to acquire a first value relating to a driving torque of the first driving motor and a second value relating to a driving torque of the second driving motor in the first state, and acquire a third value relating to the driving torque of the first driving motor and a fourth value relating to the driving torque of the second driving motor in the second state, calculate a variation amount, the variation amount being an amount of variation of the third value and the fourth value with respect to the first value and the second value, and obtain and set a relative speed of the belt image bearer and the transfer member, such that the calculated variation amount is less than a predetermined variation amount; and acquire a first value relating to a driving torque of the first driving motor and a second value relating to a driving torque of the second driving motor in the first state, and acquire a third value relating to the driving torque of the first driving motor and a fourth value relating to the driving torque of the second driving motor in the second state, calculate a variation amount, the variation amount being an amount of variation of the third value and the fourth value with respect to the first value and the second value, and obtain and set a relative speed of the belt image bearer and the transfer member, such that the calculated variation amount is less than a predetermined variation amount; and a control unit configured to control the first driving motor and the second driving motor such that the belt image bearer and the transfer member are rotated at rotational speeds corresponding to the relative speed set by the relative speed setting unit in the second state.