A light valve device includes a light valve disposed adjacent to a circuit board, and a heat-dissipating structure including a heat-dissipating main body and a heat-dissipating block. The heat-dissipating main body is disposed opposite to the light valve, and is formed with a groove defined by a first contacting surface and two engaging surfaces. The first contacting surface extends in a longitudinal direction perpendicular to the vertical direction and has two opposite longitudinal edges. The engaging surfaces respectively extend from the longitudinal edges and define an open side of the groove opposite to the first contacting surface in the vertical direction. The open side has a width in the transverse direction smaller than that of the first contacting surface. An engaging portion of the heat-dissipating block is disposed in the groove so that a second contacting surface is in contact with the first contacting surface.