A scroll fluid machine comprising: - a sealed vessel; - a first fixed scroll that is disposed so as to partition off an upper portion space inside the sealed vessel, and in which a first spiral tooth and a first spiral groove are formed on a lower surface of a first base plate; - an orbiting scroll that is configured such that an upper spiral tooth and an upper spiral groove, and a lower spiral tooth and a lower spiral groove, are formed on two surfaces of a third base plate, and that is disposed so as to face a lower surface side of the first fixed scroll such that the upper spiral tooth intermeshes with the first spiral tooth; - a second fixed scroll that is configured such that a second spiral tooth and a second spiral groove are formed on an upper surface of a second base plate, that is disposed so as to face a lower surface side of the orbiting scroll such that the second spiral tooth intermeshes with the lower spiral tooth, and that partitions off a lower portion space inside the sealed vessel; and - a main shaft that is disposed so as to be rotatably supported by a first shaft bearing portion of the first fixed scroll and a second shaft bearing portion of the second fixed scroll, and so as to pass through a boss portion of the orbiting scroll, and that makes the orbiting scroll perform orbital motion, - wherein the orbiting scroll compresses or expands a working fluid on each of an upper surface side and a lower surface side of the orbiting scroll by performing the orbital motion relative to the first and second fixed scroll (52, 51), - whereby ports (40b, 35b) that allow the working fluid to enter or leave are disposed on the first base plate and the second base plate so as to have openings next to the inner end, in the circumferential direction, of each of the first spiral tooth and the second spiral tooth, and characterized in that further ports (40a, 35a) are disposed radially inward from a radially inwardly facing side surface of each of the first spiral tooth and the second spiral tooth, the further ports (40a, 35a) are at a position that is separated from the inner end of each of the first spiral tooth and the second spiral tooth by an involute angle of 90°. - a sealed vessel; - a first fixed scroll that is disposed so as to partition off an upper portion space inside the sealed vessel, and in which a first spiral tooth and a first spiral groove are formed on a lower surface of a first base plate; - an orbiting scroll that is configured such that an upper spiral tooth and an upper spiral groove, and a lower spiral tooth and a lower spiral groove, are formed on two surfaces of a third base plate, and that is disposed so as to face a lower surface side of the first fixed scroll such that the upper spiral tooth intermeshes with the first spiral tooth; - a second fixed scroll that is configured such that a second spiral tooth and a second spiral groove are formed on an upper surface of a second base plate, that is disposed so as to face a lower surface side of the orbiting scroll such that the second spiral tooth intermeshes with the lower spiral tooth, and that partitions off a lower portion space inside the sealed vessel; and - a main shaft that is disposed so as to be rotatably supported by a first shaft bearing portion of the first fixed scroll and a second shaft bearing portion of the second fixed scroll, and so as to pass through a boss portion of the orbiting scroll, and that makes the orbiting scroll perform orbital motion, - wherein the orbiting scroll compresses or expands a working fluid on each of an upper surface side and a lower surface side of the orbiting scroll by performing the orbital motion relative to the first and second fixed scroll (52, 51), - whereby ports (40b, 35b) that allow the working fluid to enter or leave are disposed on the first base plate and the second base plate so as to have openings next to the inner end, in the circumferential direction, of each of the first spiral tooth and the second spiral tooth, and