A stent delivery system (10, 100, 150, 202, 232) comprising: an inner tube; a stent which is compressed toward a center axis and disposed on a distal side of the inner tube at the time of insertion into a lumen of a living body, and which can be restored into its pre-compression shape by expanding outward when put indwelling in the lumen of the living body; an outer tube which is disposed on an outer surface side of the inner tube, can contain the stent in its lumen, and can release the stent to the exterior by moving proximally relative to the inner tube; an operating unit (18, 102, 152, 204, 234) for moving the outer tube in an axial direction relative to the inner tube, the operating unit (18, 102, 152, 204, 234) including a rotary body (40, 44, 104, 106, 108, 164, 208, 238) which is rotated by an operation performed by an operator, and a displacement body (36, 120, 158, 220, 244) which is connected to the outer tube and is provided so as to be movable in the axial direction, characterized by a speed change mechanism (66, 110, 166, 200, 230) which is provided between the rotary body (40, 44, 104, 106, 108, 164, 208, 238) and the displacement body (36, 120, 158, 220, 244) and changes the speed of the rotation of the rotary body (40, 44, 104, 106, 108, 164, 208, 238), thereby changing the moving speed of the displacement body (36, 120, 158, 220, 244) by transmitting the rotation to the displacement body (36, 120, 158, 220, 244); the speed change mechanism (66, 110, 166, 200, 230) is rotated together with the rotary body (40, 44, 104, 106, 108, 164, 208, 238) and of which each of the diameters is changed continuously or gradually along rotary shafts (62, 118, 168) of the rotary body (40, 44, 104, 106, 108, 164, 208, 238) including a plurality of speed change portions (38, 42, 112, 114, 116, 160, 162, 210, 212, 240), and a transmission portion (56, 58, 122, 124, 126, 154, 156, 246) which is provided on the displacement body (36, 120, 158, 220, 244) and which face each of the plurality of speed change portions (38, 42, 112, 114, 116, 160, 162, 210, 212, 240) and which is meshed with or is in sliding contact with the plurality of speed change portions (38, 42, 112, 114, 116, 160, 162, 210, 212, 240). an inner tube; a stent which is compressed toward a center axis and disposed on a distal side of the inner tube at the time of insertion into a lumen of a living body, and which can be restored into its pre-compression shape by expanding outward when put indwelling in the lumen of the living body; an outer tube which is disposed on an outer surface side of the inner tube, can contain the stent in its lumen, and can release the stent to the exterior by moving proximally relative to the inner tube; an operating unit (18, 102, 152, 204, 234) for moving the outer tube in an axial direction relative to the inner tube, the operating unit (18, 102, 152, 204, 234) including the operating unit (18, 102, 152, 204, 234) including a rotary body (40, 44, 104, 106, 108, 164, 208, 238) which is rotated by an operation performed by an operator, and a displacement body (36, 120, 158, 220, 244) which is connected to the outer tube and is provided so as to be movable in the axial direction, characterized by a speed change mechanism (66, 110, 166, 200, 230) which is provided between the rotary body (40, 44, 104, 106, 108, 164, 208, 238) and the displacement body (36, 120, 158, 220, 244) and changes the speed of the rotation of the rotary body (40, 44, 104, 106, 108, 164, 208, 238), thereby changing the moving speed of the displacement body (36, 120, 158, 220, 244) by transmitting the rotation to the displacement body (36, 120, 158, 220, 244); the speed change mechanism (66, 110, 166, 200, 230) is rotated together with the rotary body (40, 44, 104, 106, 108, 164, 208, 238) and of which each of the diameters is changed continuously or gradually along rotary shafts (62, 118, 168) of the rotary body (40, 44, 104, 106, 108, 164, 208, 238) including a plurality of speed change portions (38, 42, 112, 114, 116, 160, 162, 210, 212, 240), and the speed change mechanism (66, 110, 166, 200, 230) is rotated together with the rotary body (40, 44, 104, 106, 108, 164, 208, 238) and of which each of the diameters is changed continuously or gradually along rotary shafts (62, 118, 168) of the rotary body (40, 44, 104, 106, 108, 164, 208, 238) including a plurality of speed change portions (38, 42, 112, 114, 116, 160, 162, 210, 212, 240), and a transmission portion (56, 58, 122, 124, 126, 154, 156, 246) which is provided on the displacement body (36, 120, 158, 220, 244) and which face each of the plurality of speed change portions (38, 42, 112, 114, 116, 160, 162, 210, 212, 240) and which is meshed with or is in sliding contact with the plurality of speed change portions (38, 42, 112, 114, 116, 160, 162, 210, 212, 240).