An extending and retracting device for a vehicle step includes a mounting bracket adapted to be fixed to a body of a vehicle and a step bracket. An arc sliding member is fixed to the step bracket. A driving arm defines a pair of ends thereof pivotally connected to the mounting bracket and step bracket, respectively. A supporting arm defines an upper end portion thereof pivotally connected to the mounting bracket and a lower end portion of the supporting arm defining at least one arc slot of the lower end portion. The arc sliding member is adapted to fit into the arc slot so as to be slidable in the arc slot such that the lower end portion of the supporting arm is slidably connected to the step bracket.