A shaft sealing structure for sealing a gap between a rotation shaft of a screw rotor and a housing enclosing the rotation shaft with a clearance therebetween, wherein the rotation shaft is supported by a bearing, comprising: the rotation shaft; the screw rotor; a first flange (6, 7, 9, 10, 11, 15) that projects from the housing toward the rotation shaft and is provided with an annular seal surface perpendicular to the rotation shaft; a second flange (5, 6, 7, 8, 10, 14) that projects from the housing toward the rotation shaft and is provided with a support surface opposing the seal surface; a seal ring that is arranged between said first flange (5, 6, 7, 9, 10, 11) and said second flange (6, 7, 8, 10, 14) and has an inner diameter slightly larger than an outer diameter of the rotation shaft; an energizing member that is arranged between said seal ring and the support surface and presses said seal ring against the seal surface, a plurality of shaft sealing portions each having the combination of said first flange (6, 7, 9, 10, 11, 15), said second flange (5, 6, 7, 8, 10, 14), said seal ring, and said energizing member, wherein the housing is provided with a seal fluid channel that supplies a seal fluid to a supply space formed between neighboring ones of said seal rings, wherein: the housing is provided with a discharge channel (20, 21) for communicating a discharge space formed between neighboring ones of said seal rings with a low pressure space lower in pressure than the seal fluid; characterized in that the discharge space is located on a screw rotor side with respect to the supply space. the rotation shaft; the screw rotor; a first flange (6, 7, 9, 10, 11, 15) that projects from the housing toward the rotation shaft and is provided with an annular seal surface perpendicular to the rotation shaft; a second flange (5, 6, 7, 8, 10, 14) that projects from the housing toward the rotation shaft and is provided with a support surface opposing the seal surface; a seal ring that is arranged between said first flange (5, 6, 7, 9, 10, 11) and said second flange (6, 7, 8, 10, 14) and has an inner diameter slightly larger than an outer diameter of the rotation shaft; an energizing member that is arranged between said seal ring and the support surface and presses said seal ring against the seal surface, a plurality of shaft sealing portions each having the combination of said first flange (6, 7, 9, 10, 11, 15), said second flange (5, 6, 7, 8, 10, 14), said seal ring, and said energizing member, wherein the housing is provided with a seal fluid channel that supplies a seal fluid to a supply space formed between neighboring ones of said seal rings, wherein: the housing is provided with a discharge channel (20, 21) for communicating a discharge space formed between neighboring ones of said seal rings with a low pressure space lower in pressure than the seal fluid; characterized in that the discharge space is located on a screw rotor side with respect to the supply space. the housing is provided with a discharge channel (20, 21) for communicating a discharge space formed between neighboring ones of said seal rings with a low pressure space lower in pressure than the seal fluid; characterized in that the discharge space is located on a screw rotor side with respect to the supply space.