A rotary machine system includes: a rotary machine including a gas seal portion; a gas seal device connected to the rotary machine and that supplies a seal gas to the gas seal portion; and a connecting pipe that connects the gas seal portion and the gas seal device. The rotary machine includes a casing through which a working fluid flows; a rotatable rotary shaft; and the gas seal portion that seals the working fluid by the seal gas having a pressure higher than a pressure of the working fluid in the casing. The gas seal device includes: a seal gas supply pipe through which the seal gas delivered to the connecting pipe flows; a pressure regulating valve provided in the seal gas supply pipe and that adjusts the pressure of the seal gas supplied to the gas seal portion; and a control part.