An oximeter includes a main body defining an opening and a finger clamping device arranged in the opening. The finger clamping device includes a shell, an upper clamping member, and a lower clamping member. The shell includes an inner wall carrying a sliding rail. The upper clamping member is arranged in the shell and defines a spindle. A portion of the spindle is received in the sliding rail and can slide along the sliding rail. The lower clamping member faces the upper clamping member and is coupled to the upper clamping member by a torsion spring. A finger being inserted between the upper clamping member and the lower clamping member causes the torsion spring to stretch, the finger is thus clamped by the upper clamping member and the lower clamping member with an elastic restoring force.
