A crash box for a vehicle, which mediates a back beam and a side member disposed in a width direction of the vehicle and absorbs crash energy when a crash occurs, may include a connecting body including a front coupling portion coupled to the back beam, a pair of side connecting portions bent from the front coupling portion to face each other, and a rear coupling portion extending from an end portion of each of the side connecting portions by being bent to be coupled to the side member; and a pair of connecting plates coupled to open upper and lower end portions of the connecting body, respectively.