A belt-type stepless transmission comprising: a first shaft; a first pulley having a first stationary sheave fixed to the fist shaft and a first movable sheave supported on the first shaft so as to be slidable along the axis of the first shaft and so as not to be rotatable relative to the first shaft; a second shaft arranged in parallel to the first shaft; a second pulley having a second stationary sheave fixe to the second shaft and a second movable sheave supported on the second shaft so as to be slidable along the axis of the second shaft and so as not to be rotatable relative to the second shaft; a belt wound round the first pulley and the second pulley; a third shaft arranged coaxially to the second shaft; a cam mechanism which has a sheave-side cam fixed to the second movable sheave and a shaft-side cam fixed to the third shaft and makes the sheave-side cam and the shaft-side cam touch with each other so as to enable transmission of a torque between the second movable sheave and the third shaft and to apply a biasing force corresponding to the torque on the second movable sheave; and a spring contacting the second movable sheave at one end thereof so as to bias the second movable sheave toward the second stationary sheave, characterized in that the third shaft has an inner cylinder and an outer cylinder surrounding the inner cylinder at a distance along a radial direction so as to have a gap (61 a) between the inner and outer cylinders (61, 62), an axial end portion of the second shaft is inserted into the inner cylinder and is guided and supported so as to be rotatable relative to the third shaft, and the spring is inserted at the other end thereof into the gap (61 a) between the outer 2cylinder and the inner cylinder and is supported by the third shaft so as to be able to extend and retract along the axial direction along with the axial movement of the second movable sheave relative to the second shaft. a first shaft; a first pulley having a first stationary sheave fixed to the fist shaft and a first movable sheave supported on the first shaft so as to be slidable along the axis of the first shaft and so as not to be rotatable relative to the first shaft; a second shaft arranged in parallel to the first shaft; a second pulley having a second stationary sheave fixe to the second shaft and a second movable sheave supported on the second shaft so as to be slidable along the axis of the second shaft and so as not to be rotatable relative to the second shaft; a belt wound round the first pulley and the second pulley; a third shaft arranged coaxially to the second shaft; a cam mechanism which has a sheave-side cam fixed to the second movable sheave and a shaft-side cam fixed to the third shaft and makes the sheave-side cam and the shaft-side cam touch with each other so as to enable transmission of a torque between the second movable sheave and the third shaft and to apply a biasing force corresponding to the torque on the second movable sheave; and a spring contacting the second movable sheave at one end thereof so as to bias the second movable sheave toward the second stationary sheave, characterized in that the third shaft has an inner cylinder and an outer cylinder surrounding the inner cylinder at a distance along a radial direction so as to have a gap (61 a) between the inner and outer cylinders (61, 62), an axial end portion of the second shaft is inserted into the inner cylinder and is guided and supported so as to be rotatable relative to the third shaft, and the spring is inserted at the other end thereof into the gap (61 a) between the outer 2cylinder and the inner cylinder and is supported by the third shaft so as to be able to extend and retract along the axial direction along with the axial movement of the second movable sheave relative to the second shaft.