To provide a dead-man brake of an automatic track bicycle can reliably keep a stopped state and free from any overrun state.

A brake piece driving means to retract a brake piece 6 provided on a vehicle body 2 in an advancing/retractable manner when a person is seated on a seat 4 and advance the brake piece when the person is separated therefrom is provided between the seat 4 provided on the vehicle body 2 supported by front and rear pairs of wheels 1, 1' and an axle 5 between the front wheels 1 or the rear wheels 1'. Recessed parts 9 with a fore end 6a of the brake piece 6 being engaged/disengaged therewith/therefrom are formed in a row in a circumferential end face 8' along the concentric circle with the axle 5 of a brake disk 8 provided on the axle 5.