The present invention relates to a sheet-like light source device, including a light-conducting plate having at least one convex portion disposed on the lateral portion thereof; at least one light-source unit disposed on one side of the light-conducting plate, which includes a light source and a reflecting sheet; and a housing having a chassis and at least one frame; in which the frame is mounted on the edges of the chassis, and a concave portion corresponding to the convex portion of the light-conducting plate to hold the convex portion and a plurality of light-guiding mechanisms are formed on the frame. The present invention further has a housing for a sheet-like light source device, including a chassis and a frame mounted on the edges of the chassis, in which a concave portion and a plurality of light-guiding mechanisms are formed on the frame.