Provided is an engine that includes a first member, a second member, a first hydraulic pressure chamber formed between facing parts of the first and second members, and a hydraulic pressure adjustment mechanism. The hydraulic pressure adjustment mechanism has a plunger pump having a pump cylinder and a plunger 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.