The present invention is directed to a multiply convertible bicycle exercise apparatus, and intends to provide a multiply convertible bicycle exercise apparatus that allows the form of a bicycle exercise apparatus to be freely converted into various forms such as standing, sitting, dancing, and riding forms, so that various types of exercise can be enjoyed, various types of exercise apparatuses can be replaced with a single exercise apparatus, and the shape and size of the exercise apparatus can be adjusted to fit the physical size of a user even in a converted state, and that changes the location of the center of gravity of the bicycle exercise apparatus from the existing lower portion to the upper portion where a user's groin is located, so that the bicycle exercise apparatus is stable in connection with the center of gravity and is superior in terms of stability.