A bike having an expanded knife ski device includes left and right landing wheel arms on the left and right portions of the bike, respectively. Left and right landing wheels are rotatably coupled to the lower end of the left and right landing wheel arm, respectively, to move the landing wheels up and down. Left and right driving units lift and lower the left and right landing wheels, respectively. Left and right ski mounting sockets are coupled to the left and right landing wheel arms, respectively. Left and right insertion members couple to the left and right ski mounting sockets, respectively. Left and right ski legs are integrally coupled to the left and right insertion members, respectively, to extend downwards. Left and right bike skis, which are hinge-coupled to the lower end of the left and right ski legs, respectively, each making a hinge movement about a left/right horizontal axis.