Abstract: There is provided an auxiliary device for abdominal muscle exercise, and more particularly, to an auxiliary device for abdominal muscle exercise having a simple shape in which two supports are connected to each other by a board for easily exercising and strengthening the body. To achieve the objects of the present invention, the auxiliary device for abdominal muscle exercise comprises: a first support (3) being of a predetermined height and size sufficient to support the sacral region just beneath the lumbar region in use; a board (5) secured to and extending from the bottom surface of the first support (3); and a second support (7) secured to and positioned on the end of the board (5) opposite to the first support (3). Preferably, the width of the board (5) [the shortest distance between the first support (3) and the second support (7)] and the height and inclination of the second support (7) may be formed to support the lesser trochanter region of the femur.