Provided is an engine that includes a first member (piston rod (112a)), a second member (crosshead pin (114a)), a first hydraulic pressure chamber (168a) formed between facing parts of the first and second members, and a hydraulic pressure adjustment mechanism (196). The hydraulic pressure adjustment mechanism has a plunger pump (182) having a pump cylinder (182a) and a plunger (182b) and configured to supply hydraulic oil in the pump cylinder to the first hydraulic pressure chamber by pushing the plunger into the pump cylinder. The plunger pump moves in a stroke direction along with a piston and a power transmission section, and the plunger is pushed into the pump cylinder by receiving a reaction force opposite to reciprocating forces of the piston and the power transmission section.