Abstract: The exercise bike includes a main frame, a handlebar, a driving wheel, a rotary wheel, a seat and a housing. The rotary wheel has a circular driving element eccentrically disposed at one side thereof. The driving element is provided with a driving arm and is secured in place by a positioning element. The driving arm has one end provided with a pivot hole. The seat has an elevating rod disposed below, which is mounted to the rear of the main frame by means of a tube such that the elevating rod may displace within the tube. Below the elevating rod are provided a spring and a stop rod for connecting with the pivot hole of the driving arm via a pivot element. The exercise bike utilizes the user's weight to act as an exercising load to provide resistance and enables the user to rise and fall rhythmically with the rotation of the bike.