Edited by Haruki NakamuraThe Novel Prize in Chemistry 2016 was awarded for "Design and production of molecular machines". Many molecular machines, molecules that move like machines on the nanoscale, have been successfully synthesized and methods to produce mechanical motions have been developed. On the other hand, it has been suggested that various functions are produced by introducing the function "converting energy" to "molecular mechanical motions". Five years ago, pioneer researchers defined such molecular machines, which have the function of energy conversion, as "Molecular Engine". They have researched energy conversion mechanisms of biomolecular machines in detail, understood the essence and general law by physics, and synthesized artificially "Molecular Engines" by chemistry. "Molecular Engine", design of autonomous functions through energy conversion, has buded by the orchestration of chemists, biologists, and physicists in the last five years supported by Grant-in-Aid for Scientific Research on Innovative Areas (18H05418).This scientific concept should be passed down to the next generations for further development. To this end, early-career researchers in various research fields are trying to elucidate the energy conversion mechanism of molecular machines and to design novel ones. Here, we invite eight early-career researchers who will lead the field in the future and have a symposium at the 60 th Annual Meeting of the Biophysical Society of Japan held in September 2022.Four researchers talk about researches of biological "Molecular Engine". By learning a detailed energy conversion mechanism from natural molecular engines, we will obtain guidelines for the design of "Molecular Engine". Dr. Maria del Carmen Marin at the University of Tokyo focuses on the ion transport mechanism of an outward-directed light-driven H + pumping microbial rhodopsin, PspR. From the structural insight [1], she has succeeded in creating PspR mutants which pump H + inwardly. Dr. Ryohei Kobayashi and Dr. Akihiro Otomo present on rotary ATPases, the most abundant biological molecular engine. Dr. Kobayashi at Institute for Molecular Science reports a detailed mechanism of a regulatory protein for mitochondrial ATP synthase, IF1. One of the unique features of IF1 is the unidirectional regulation, that is, it inhibits ATP hydrolysis but does not inhibit ATP synthesis. He elucidated the unidirectional regulation system