A surfing exerciser includes a seat, a seat frame, a chassis, a swing device, and a torsion spring. The seat is secured on the seat frame. The swing device includes an upper freewheel, a lower freewheel, a Z-shaped swivel shaft, a small pulley shaft, and a belt. The Z-shaped swivel shaft includes a lower swivel shaft, an upper swivel shaft, and a connecting board. The lower swivel shaft is fixed to a lower surface of the connecting board. The upper swivel shaft is fixed to an upper surface of the connecting board. The axis of the lower swivel shaft obliquely intersects with the axis of the upper swivel shaft. By the rotation inertia of the upper freewheel and the lower freewheel, the seat of the present invention is driven to move up and down as well as left and right for providing surfing or horse riding simulation.