To obtain an underwater pedometer which conveniently counts the number of steps when walking under water.

When a foot to which an underwater pedometer 1 is fixed is pushed forward under water, water is caused to flow into a water flow chamber 5, a webbing plate (24) receives the water pressure of the flowing water and a webbing bar 18 is shaken. When the shaking quantity of the bar 18 becomes a prescribed value, a movable electrode 27 is brought into contact with a fixed electrode 28. The contact signal is inputted to a counter 31. The counter 31 adds the number of steps of a foot to which the pedometer 1 is not fixed to the detection signal and performs counting. The counting results of the counter 31 are shown by a displaying means (32). The numeric value shown by the means (32) is one that doubles the number of steps of the foot to which the pedometer 1 is fixed and becomes the actual number of steps of a person moving under water. Further, when the leg to which the pedometer 1 is fixed stops moving, the bar 18 is made to move toward a neutral position due to the weight of the plate (24), and the contact state of the electrodes 27 and 28 is released.