An optical semiconductor apparatus comprising: a package substrate that includes a recess being open on a top surface of the package substrate; an optical semiconductor device housed in the recess; a window member provided to cover an opening of the recess; and a sealing structure for sealing a space between the package substrate and the window member, wherein the sealing structure includes a first metal layer provided in a shape of a frame on the top surface of the package substrate, a second metal layer provided in a shape of a frame on an inner surface of the window member, and a metal bonding part provided between the first metal layer and the second metal layer, wherein: the sealing structure is configured such that an entirety of the second metal layer is positioned in a region where the first metal layer is provided, and the metal bonding part is positioned on both sides sandwiching the second metal layer, an outer dimension (w 11) of the first metal layer is larger than an outer dimension (w 21) of the second metal layer, and an inner dimension (w 12) of the first metal layer is smaller than an inner dimension (w 22) of the second metal layer, characterized in that an inner dimension difference (w 22 -w 12) between the first metal layer and the second metal layer being larger than an outer dimension difference (w 11 -w 21) between the first metal layer and the second metal layer. a package substrate that includes a recess being open on a top surface of the package substrate; an optical semiconductor device housed in the recess; a window member provided to cover an opening of the recess; and a sealing structure for sealing a space between the package substrate and the window member, wherein the sealing structure includes a first metal layer provided in a shape of a frame on the top surface of the package substrate, a second metal layer provided in a shape of a frame on an inner surface of the window member, and a metal bonding part provided between the first metal layer and the second metal layer, wherein: the sealing structure is configured such that an entirety of the second metal layer is positioned in a region where the first metal layer is provided, and the metal bonding part is positioned on both sides sandwiching the second metal layer, an outer dimension (w 11) of the first metal layer is larger than an outer dimension (w 21) of the second metal layer, and an inner dimension (w 12) of the first metal layer is smaller than an inner dimension (w 22) of the second metal layer, characterized in that an inner dimension difference (w 22 -w 12) between the first metal layer and the second metal layer being larger than an outer dimension difference (w 11 -w 21) between the first metal layer and the second metal layer. the sealing structure is configured such that an entirety of the second metal layer is positioned in a region where the first metal layer is provided, and the metal bonding part is positioned on both sides sandwiching the second metal layer, an outer dimension (w 11) of the first metal layer is larger than an outer dimension (w 21) of the second metal layer, and an inner dimension (w 12) of the first metal layer is smaller than an inner dimension (w 22) of the second metal layer, characterized in that an inner dimension difference (w 22 -w 12) between the first metal layer and the second metal layer being larger than an outer dimension difference (w 11 -w 21) between the first metal layer and the second metal layer.