The present invention relates to a wheelchair brake system, and more particularly to a wheelchair brake system which is in a brake lock mode as usual as when a user stands up from a wheelchair, but automatically releases a brake only if a user sits down on the wheelchair or folds up the wheelchair, so that the wheelchair can move only when a user sits down thereon or it is folded, thereby preventing a user from getting hurt from a fall at a moment when the user sits down on and stands up from the wheelchair.
