A step-by-step motor able to carry out up-and-down transmission includes a housing, a top rod, a circuit board, a magnet, a coil unit and a cover. The top rod is inserted in an insert hole of the housing, having a wall bored with a cut recess. The circuit board has a position-limiting switch received in an engage groove of the housing and provided with a sidewise rod inserted in the cut recess of the top rod. The magnet is fixed with a connecting member connecting a bearing, and the lower end of the top rod is engaged with the connecting member. The coil unit is fitted around the magnet and positioned in the housing, and the cover is covered on the bottom of the housing. The magnet is driven by the coil unit to rotate and actuate the top rod to move upward or downward steadily.