A work in progress includes: a pair of glass substrates arranged to face each other; a peripheral wall having a frame shape and disposed between the pair of glass substrates; a boundary wall; and an evacuation port. The boundary wall hermetically separates an internal space, surrounded with the pair of glass substrates and the peripheral wall, into an evacuation space, a buffer space, and a ventilation space. The evacuation port connects the ventilation space to an external environment. The evacuation space and the buffer space have a lower internal pressure than the ventilation space. A predetermined part, including the evacuation space but excluding parts covering the buffer space and the ventilation space, of the work in progress, forms the glass panel unit.