A surgical instrument (1, 1A), comprising: a treatment section configured to treat a treatment target; a first pulling section configured to transmit a pulling force to the treatment section to operate the treatment section; a second pulling section configured to transmit a pulling force to the treatment section to operate the treatment section; a power source configured to generate force for operating the treatment section; and a switching section (15, 15A) having a first path configured to transmit the force from the power source to the first pulling section, a second path configured to transmit the force from the power source to the second pulling section, a first engaging body to which the first pulling section is connected, and second engaging body to which the second pulling section is connected, the switching section (15, 15A) being configured to switch the first path and the second path, wherein the first pulling section has a first pulling member that is flexible and connected to the treatment section, and the second pulling section has a second pulling member that is flexible and connected to the treatment section, characterized in that the treatment section includes a grasping forceps that is configured to swing by an operation rotating around a pivotal shaft, wherein distal ends of the first pulling section and the second pulling section are connected to the pivotal shaft and the first pulling section and the second pulling section are wound on an outer circumferential surface of the pivotal shaft and pulled to be swung; and wherein the first engaging body is a first rack section (20, 30A) to which the first pulling member is fixed, the second engaging body is a second rack section (21, 35A) to which the second pulling member is fixed, and the switching section (15, 15A) has: a pinion configured to be capable of meshing with the first rack section (20, 30A) and the second rack section (21, 35A); a moving section configured to move the pinion to switch between a first transmission state and a second transmission state, the first transmission state being a state in which the first rack section (20, 30A) is meshed with the pinion and the second rack section (21, 35A) is spaced from the pinion, and the second transmission state being a state in which the second rack section (21, 35A) is meshed with the pinion and the first rack section (20, 30A) is spaced from the pinion; and a transmission section configured to transmit the force from the power source to the pinion. a treatment section configured to treat a treatment target; a first pulling section configured to transmit a pulling force to the treatment section to operate the treatment section; a second pulling section configured to transmit a pulling force to the treatment section to operate the treatment section; a power source configured to generate force for operating the treatment section; and a switching section (15, 15A) having a first path configured to transmit the force from the power source to the first pulling section, a second path configured to transmit the force from the power source to the second pulling section, a first engaging body to which the first pulling section is connected, and second engaging body to which the second pulling section is connected, the switching section (15, 15A) being configured to switch the first path and the second path, wherein the first pulling section has a first pulling member that is flexible and connected to the treatment section, and the second pulling section has a second pulling member that is flexible and connected to the treatment section, characterized in that the treatment section includes a grasping forceps that is configured to swing by an operation rotating around a pivotal shaft, wherein distal ends of the first pulling section and the second pulling section are connected to the pivotal shaft and the first pulling section and the second pulling section are wound on an outer circumferential surface of the pivotal shaft and pulled to be swung; and wherein the first engaging body is a first rack section (20, 30A) to which the first pulling member is fixed, the second engaging body is a second rack section (21, 35A) to which the second pulling member is fixed, and the switching section (15, 15A) has: a pinion configured to be capable of meshing with the first rack section (20, 30A) and the second rack section (21, 35A); a moving section configured to move the pinion to switch between a first transmission state and a second transmission state, the first transmission state being a state in which the first rack section (20, 30A) is meshed with the pinion and the second rack section (21, 35A) is spaced from the pinion, and the second transmission state being a state in which the second rack section (21, 35A) is meshed with the pinion and the first rack section (20, 30A) is spaced from the pinion; and a transmission section configured to transmit the force from the power source to the pinion. a pinion configured to be capable of meshing with the first rack section (20, 30A) and the second rack section (21, 35A); a moving section configured to move the pinion to switch between a first transmission state and a second transmission state, the first transmission state being a state in which the first rack section (20, 30A) is meshed with the pinion and the second rack section (21, 35A) is spaced from the pinion, and the second transmission state being a state in which the second rack section (21, 35A) is meshed with the pinion and the first rack section (20, 30A) is spaced from the pinion; and a transmission section configured to transmit the force from the power source to the pinion.