A brake device for a pushcart includes a main movable member disposed movably within a main seat, an auxiliary movable member disposed movably within an auxiliary seat, and a connecting member interconnecting the main and auxiliary movable members. The main movable member is biased to an upper limit position, and is movable to a lower limit position so as to engage a main brake pin with a groove in a main pin-engaging member that is connected fixedly to one wheel. Hence, the connecting member moves the auxiliary movable member from a first position to a second position so as to engage an auxiliary brake pin with a groove in an auxiliary pin-engaging member that is connected fixedly to another wheel. As a result, the wheels are locked.