An optical device cavity structure includes: insulator layers and metal layers alternately layered on one another; a first terminal section which is formed on a mounting surface to be mounted on a wiring substrate and which is electrically connected to the wiring substrate; a cavity portion having a generally rectangular opening formed in a central portion of the upper surface; and a light-transmitting member placement section formed on the upper surface surrounding the opening for receiving a light-transmitting member thereon, wherein the light-transmitting member is for transmitting therethrough light to be received by, or light emitted from, an optical element chip.