A vehicle body reinforcement device being configured to be supported on a vehicle body via first and second brackets (BR1, BR2) that are disposed at opposing ends of the vehicle body in an axial direction of the vehicle body reinforcement device, comprising: a housing being connected to one of the first bracket and the second bracket, the housing including a first retaining portion and a second retaining portion each disposed at an inner portion of the housing, the inner portions that are spaced apart from each other by a predetermined distance in the axial direction; a first shaft member being contained in the housing and including a first end portion that is supported so as to be approachable and separable relative to the first retaining portion; a second shaft member including a first end portion that is connected to a second end portion of the first shaft member, the second shaft member including a second end portion that is connected to the other of the first bracket and the second bracket; a first biasing member being provided between the first end portion of the first shaft member and the first retaining portion; a second biasing member being provided between the second end portion of the first shaft member and the second retaining portion; a pressing member supported on the first shaft member so as to be movable in a direction orthogonal to an axis of the first shaft member within the housing and to be contactable with an inner surface of the housing, the pressing member pressing the inner surface of the housing; and an adjustment member being supported on the first shaft member, the adjustment member adjusting a pressing force applied by the pressing member against the inner surface of the housing; characterized in that the first shaft member includes a thread hole being formed in the direction orthogonal to the axis of the first shaft member; and a recess being continuously formed with the thread hole and containing the pressing member; the housing includes a second opening portion being disposed at a predetermined position opposing the recess and facing the thread hole; and the adjustment member includes a male thread portion threaded into the thread hole; and a rotary operation head portion being continuously formed with the male thread portion, the rotary operation head portion being formed at a side where the second opening portion is provided. a housing being connected to one of the first bracket and the second bracket, the housing including a first retaining portion and a second retaining portion each disposed at an inner portion of the housing, the inner portions that are spaced apart from each other by a predetermined distance in the axial direction; a first shaft member being contained in the housing and including a first end portion that is supported so as to be approachable and separable relative to the first retaining portion; a second shaft member including a first end portion that is connected to a second end portion of the first shaft member, the second shaft member including a second end portion that is connected to the other of the first bracket and the second bracket; a first biasing member being provided between the first end portion of the first shaft member and the first retaining portion; a second biasing member being provided between the second end portion of the first shaft member and the second retaining portion; a pressing member supported on the first shaft member so as to be movable in a direction orthogonal to an axis of the first shaft member within the housing and to be contactable with an inner surface of the housing, the pressing member pressing the inner surface of the housing; and an adjustment member being supported on the first shaft member, the adjustment member adjusting a pressing force applied by the pressing member against the inner surface of the housing; characterized in that the first shaft member includes a thread hole being formed in the direction orthogonal to the axis of the first shaft member; and a recess being continuously formed with the thread hole and containing the pressing member; a thread hole being formed in the direction orthogonal to the axis of the first shaft member; and a recess being continuously formed with the thread hole and containing the pressing member; the housing includes a second opening portion being disposed at a predetermined position opposing the recess and facing the thread hole; and the adjustment member includes a male thread portion threaded into the thread hole; and a rotary operation head portion being continuously formed with the male thread portion, the rotary operation head portion being formed at a side where the second opening portion is provided. a male thread portion threaded into the thread hole; and a rotary operation head portion being continuously formed with the male thread portion, the rotary operation head portion being formed at a side where the second opening portion is provided.