Abstract: A sit-up exercising apparatus includes at least one inclined abdominal board and a counting device mounted in the abdominal board. The counting device includes a support bracket secured in the abdominal board, a magnetic detector mounted on the support bracket, a movable member movably mounted on the support bracket and movable relative to the support bracket and the magnetic detector, a magnetic member mounted on the movable member to move with the movable member and movable to pass by the magnetic detector to produce multiple magnetic signals in the magnetic detector, and a transmission wire connected with the magnetic detector to transmit the magnetic signals in the magnetic detector. Thus, the counting device can count the times of the sit-up actions automatically so that the user needs not count the sit-up times by himself/herself during the exercising process.