The invention provides a stepless speed changer. The stepless speed changer comprises an input shaft, to which the driving force of a driving source is delivered; an output shaft, which is parallel to the input shaft; and a plurality of crank connecting rod mechanisms, which comprise a rotation radius adjusting mechanism, which can rotate around the input shaft and adjust the rotation radius freely, and a swing rod, which is pivotedly arranged on the output shaft and converts the rotation movement of the input shaft into swing movement of swing rod; and a unidirectional rotation stopping mechanism. When the swing rod is about to rotate to one side relative to the output shaft, which is taken as the rotation center, the swing rod is fixed by the unidirectional rotation stopping mechanism. When the swing rod is about to rotate to the other side, the swing rod is in an idle state relative to the output shaft. Part of the periphery of the swing rod is provided with a protruded part relative to the circumferential direction. A plurality of detection parts are arranged on the peripheral side of the swing rod. The detection parts detect the distance to the external circumferential surface of the swing rod, the protruded part is included, and the difference of the detection values detected by any two detection parts changes along with the swing movement of the swing rod.