A brake adjustment body is disposed in a direction orthogonal to turning shafts between a bending drive shaft and a lock operation shaft. The brake adjustment body is configured by including an intermediate member that abuts a cam portion of the lock operation shaft, and a brake member that applies to the bending drive shaft a pressure according to displacement of the intermediate member. The intermediate member has a shaft body portion and a cylindrical sliding portion screwed together, and by rotating the sliding portion in a state where the shaft body portion and the sliding portion are screwed together, the distance between a proximal end portion and a distal end portion of the intermediate member may be adjusted, and when fixing force on the bending drive shaft is reduced, the distance may be re-adjusted to restore the fixing force.