Structure and method for sealing through-hole, and transfer substrate for sealing through-hole

A sealing structure with a surface of a base material with a through-hole, an underlying metal film, and a sealing member bonded to the underlying metal film to seal the through-hole. The sealing member includes a compressed product of a metal powder including gold having a purity of 99.9% by mass or more and a lid-like metal film including a bulk-like metal including gold and having a thickness of not less than 0.01 μm and not more than 5 μm. The sealing material includes an outer periphery-side densified region in contact with an underlying metal film and a center-side porous region in contact with the through-hole. The shape of pores in the densified region is specified, and the horizontal length (l) of a pore in the radial direction at any cross-section of the densified region and the width (W) of the densified region satisfy the relationship of l≤0.1W.