As for H-shaped beams, concrete floor slab and purlins can be considered as bracing if they have enough stiffness and strength. There are many studies about bracing against lateral torsional buckling. However, the effect of lateral bracing cannot be properly considered in the practical design currently. The purpose of this study is to show the effect of the lateral bracing and vertical stiffener experimentally. The test on the lateral buckling of H-shaped steel beam with a steel plate which is a continuous bracing is carried out. Parameters are the position of bracing and presence or absence of vertical stiffener. The steel plate is welded on the compressive flange or the tensile flange. The vertical stiffener may be considered as the bracing for lateral buckling however the effects of them are not clear. The vertical stiffener is set at the position where the lateral deformation is assumed largest. The lateral buckling and local buckling occurs in the test specimens without bracing and with continuous bracing on the tensile flange. The maximum strength of the test specimen with a vertical stiffener is 5% smaller than that of the test specimen without a vertical stiffener. However, the strength degradation of the test specimen with a vertical stiffener is smaller and the load is 90 % more than the maximum load when the rotation angle is 0.07 rad.