Biomimetic material systems using stimuli-responsive polymers and gels have been widely studied for applications to artificial muscles, drug delivery systems, biosensors, etc. In almost all cases, however, the action is driven by on-off switching of external signals. In contrast, here we show a novel biomimetic gel to exhibit autonomous self-beating motion in ATP solution under constant condition, similar to heart muscle. An anionic polymer gel with phosphoric groups, in which creatine kinase was immobilized, was prepared. When the gel was immersed in the ATP solution, the enzymatic reaction occurs in the gel and the concentration of calcium ion changes periodically. Since the chelates between phosphoric groups and the divalent calcium ion, which acts a physical crosslikning point, are formed and dissociated periodically, the gel repeats swelling and deswelling autonomously.