An abdominal exercise device has a kneeling pad and a roller. The kneeling pad includes a top surface and two spaced apart kneeling recesses. The kneeling recesses are formed in the top surface of the kneeling pad. The roller is positioned movably relative to the kneeling pad when in use and includes a bracket, a left handle, a right handle, a front wheel and two rear wheels. The left and right handles are attached to a middle of the bracket. The front wheel is mounted on a front of the bracket. The rear wheels are mounted on a rear of the bracket. The kneeling recesses are ergonomically designed to correspond to contours of the human knees, thereby providing a comfortable support for a user's knees. The three wheels ensure that the roller has good balanced performance such that the user can steadily operate the roller.