Stiffness reinforcement structure for vehicle

An embodiment stiffness reinforcement structure for a vehicle includes a support member including an upper end joined to a lateral end of a roof bow of a vehicle body and a lower end joined to a front frame disposed at a lower portion of the vehicle body to connect the roof bow and the front frame. The support member is disposed between a side pillar of the vehicle body and an interior of the vehicle body and is spaced apart from the side pillar at a lower region of the support member. The lower end of the support member is positioned further into the interior of the vehicle body than the upper end.