A stopcock for a channel that guides a flux medium in a medical endoscope, the stopcock having a housing accommodating a plug rotatable about an axis in a conical seat penetrated by the channel, wherein the housing has a bearing collar adjacent to the conical seat in the direction of the axis, in which bearing collar a handle body is mounted to be rotatable about the axis, the handle body supporting a handle outside the housing and rotationally coupled to the plug displaceable in direction of the axis and resiliently supported relative thereto, wherein the handle body has a radially elastic detent device engaging a circumferential inner groove of the bearing collar to be locking in direction of the axis, wherein the plug is arranged and configured bring the detent device out of engagement with the bearing collar upon displacement in direction of the axis into an unlocked position.