Here we present an analysis of the paper "Universelle Bedeutung des Wirkungsquantums" (The universal meaning of the quantum of action), published by Jun Ishiwara in German in the "Proceedings of Tokyo Mathematico-Physical Society 8 (1915) 106-116". In his work, Ishiwara, established in the Sendai University, Japan, proposed -simultaneously with Arnold Sommerfeld, William Wilson and Niels Bohr in Europe -the phase-space-integral quantization, a rule that would be incorporated into the old-quantum-theory formalism. The discussions and analysis render this paper fully accessible to undergraduate students of physics with elementary knowledge of quantum mechanics.