A human-powered scooter propelled by side-to-side movement of the user. The scooter has a steering mechanism coupled to a front wheel, and two frame arms pivotably coupled to the steering mechanism and extending rearward, to which two rear wheels are respectively coupled. A novel linking piece such as a mechanical plate member coupled to the steering mechanism can releasable engage with the frame arms in order to restrict their pivoting to equal magnitude in opposite directions. The linking piece can also disengage from the frame arms to allow the frame arms to be folded up. The pivoting axes of the two frame arms are predetermined such that, when folded, the frame arms are as near as possible to being parallel to a main steering control shaft of the steering mechanism. A mechanism for directly braking at least one of the rear wheels is also disclosed.