To provide a deflection preventive structure excellent in fatigue strength by alienating stress concentration.

A longitudinal member 3 constituted of a web plate 3b and a face bar 3a provided with a constant interval along the lengthy direction of an outer plate 6 passes through a slot part 1a of a lateral member 1 connected to the outer plate and arranged in a direction orthogonal with the longitudinal member 3 and is reinforced by a deflection preventive plate 2 to connect the face bar 3a of the longitudinal member 3 and the lateral member 1 on this deflection preventive structure. In this case, a gouging part 2b made of a curved surface protruded and smooth toward a side 2a on the opposite side of a side of the lateral member 1 is provided on a lower end part of the side of the lateral member 1 of the deflection preventive plate 2 which is not connected to the lateral member 1 as there exists the slot part 1a, a lower side of the deflection preventive plate 2 connected to the face bar 3a of the longitudinal member 3 below the gouging part 2b is projected to the back side of the lateral member 1 beyond the slot part 1a of the lateral member 1 and this gouging part 2b is connected to this projected part.