An energy recovery system for recovering energy from a working fluid, comprising: a fluid chamber having a variable volume and the working fluid sealed therein; an inertial fluid container, including a first internal space communicating with the fluid chamber, for receiving the working fluid discharged from the fluid chamber as the volume of the fluid chamber decreases; a low pressure container, including a second internal space set at a lower pressure than the fluid chamber and communicating with the first internal space of the inertial fluid container, for receiving the working fluid discharged from the inertial fluid container; a high pressure container, including a third internal space set at a higher pressure than the second internal space of the low pressure container and communicating with the first internal space of the inertial fluid container, for receiving the working fluid discharged from the inertial fluid container; a low pressure valve having a low pressure opening for permitting flow of the working fluid between the inertial fluid container and the low pressure container, and operable to open and close the low pressure opening; a high pressure valve having a high pressure opening for permitting flow of the working fluid between the high pressure container and the inertial fluid container, and operable to open and close the high pressure opening; a valve flow conduit (31, 32), extending from the inertial fluid container to the low pressure valve and the high pressure valve, for guiding the working fluid; and a valve controller for controlling, in response to a decrease in volume of the fluid chamber, the opening and closing operations of the high pressure valve and the low pressure valve such that the inertial fluid container alternately communicates with the low pressure container and the high pressure container, thereby generating inertial forces of the working fluid flowing toward the low pressure container in the first internal space of the inertial fluid container, and causing the working fluid to flow into the high pressure container by the inertial forces, characterised in that the valve controller sets a switching frequency for switching the inertial fluid container between communicating with the low pressure container and communicating with the high pressure container to a frequency of an Nth-order anti-resonance frequency of a flow conduit for the working fluid including at least the inertial fluid container and the valve flow conduit (31, 32), wherein in the Nth-order N is a natural number, and wherein said anti-resonance frequency is a frequency at which a working fluid flow fluctuations reach a local minimum value. a fluid chamber having a variable volume and the working fluid sealed therein; an inertial fluid container, including a first internal space communicating with the fluid chamber, for receiving the working fluid discharged from the fluid chamber as the volume of the fluid chamber decreases; a low pressure container, including a second internal space set at a lower pressure than the fluid chamber and communicating with the first internal space of the inertial fluid container, for receiving the working fluid discharged from the inertial fluid container; a high pressure container, including a third internal space set at a higher pressure than the second internal space of the low pressure container and communicating with the first internal space of the inertial fluid container, for receiving the working fluid discharged from the inertial fluid container; a low pressure valve having a low pressure opening for permitting flow of the working fluid between the inertial fluid container and the low pressure container, and operable to open and close the low pressure opening; a high pressure valve having a high pressure opening for permitting flow of the working fluid between the high pressure container and the inertial fluid container, and operable to open and close the high pressure opening; a valve flow conduit (31, 32), extending from the inertial fluid container to the low pressure valve and the high pressure valve, for guiding the working fluid; and a valve controller for controlling, in response to a decrease in volume of the fluid chamber, the opening and closing operations of the high pressure valve and the low pressure valve such that the inertial fluid container alternately communicates with the low pressure container and the high pressure container, thereby generating inertial forces of the working fluid flowing toward the low pressure container in the first internal space of the inertial fluid container, and causing the working fluid to flow into the high pressure container by the inertial forces, characterised in that the valve controller sets a switching frequency for switching the inertial fluid container between communicating with the low pressure container and communicating with the high pressure container to a frequency of an Nth-order anti-resonance frequency of a flow conduit for the working fluid including at least the inertial fluid container and the valve flow conduit (31, 32), wherein in the Nth-order N is a natural number, and wherein said anti-resonance frequency is a frequency at which a working fluid flow fluctuations reach a local minimum value.