To provide a surface cycle boat which can be propulsive through a horizontal caudal fin of high energy efficiency by a simple mechanism to mechanically reproduce an ideal caudal fin motion locus to be similar to that of a fish.

Leg parts 2a are fixed astride catamaran hulls 1, so a seat 2 on which a driver is seated is disposed. A pedal mechanism supported on the seat 2 to provide torque is disposed at a front position of the seat 2. A pair of pedals 22 are fixed to a shaft 12, and a toothed gear 13 is fixed on it. This toothed gear 13 is engaged with a toothed wheel fixed on a shaft through a power transmission means 15. A bearing is provided at an end of a caudal fin 5 through a crank arm under a crank close to a bottom part between the hulls 1, 1 to be rotatably supported through a shaft supported on a frame 26. The caudal fin 5 of a horizontal type is provided to be rotatably supported on the frame 26.