Nonadiabatic changes of the magnetic moment &mgr; in the ELMO Bumpy Torus‐Scale (EBT‐S) have been studied both analytically and numerically. Simple forms of &Dgr; &mgr; and gyrophase change were obtained, permitting the changes in these quantities to be studied using an iteration mapping. The mapping results show stochastic behavior for particles having high energy and low initial &mgr;. Otherwise, superadiabatic motion appears. The stochastic diffusion coefficient for the variation of &mgr; was measured numerically by mapping and was also calculated from quasilinear theory. The results are shown to agree well in the stochastic region. For high‐energy particles, the diffusion in &mgr; caused by nonadiabaticity can be comparable to collisional diffusion when stochastic motion occurs for EBT‐S.