The heat‐, and pressure‐induced gelation process of actomyosin was investigated by observing the transmitted light spectra. First, pH and [NaCl] dependences of the characteristic temperature (T’g) related to the gelation were determined at atmospheric pressure. Then, the temperature variations of the transmitted light spectra were monotored after the temperature‐ and pressure‐jump procedures, revealing the growth of the actomyosin assembly during these gelation processes.