A nondestructive evaluation technique based on nonlinear acoustics has been recently expected as a potential method of detecting a closed crack such as a failure of joining and a fatigue crack caused by residual stress. This research investigates nonlinearity coming from collisions between two faces of a closed crack caused by incident ultrasonic waves. According to our theoretical analysis of nonlinear dynamics shown by a simple mass-spring model hitting against a sinusoidally excited base, qualitative changes in vibration of the mass occur and superharmonics or subharmonics appear, depending on parameters such as the input frequency or the initial compression between the mass and the base. Numerical analyses and experiments were also carried out, by using a model of two solid blocks in contact. Obtained results show tendency similar to that of the above theoretical result.