A method for manufacturing a glass panel unit, the method comprising an assembling step, an evacuation step, and a sealing step, the assembling step including providing a glass panel unit assembly, the glass panel unit assembly comprising: a pair of glass substrates (200, 300) arranged to face each other; a peripheral wall having a frame shape, containing a first sealing material having a first softening point and disposed between the pair of glass substrates (200, 300); a partition containing a second sealing material having a second softening point that is higher than the first softening point and partitioning an internal space, surrounded with the pair of glass substrates (200, 300) and the peripheral wall, into a first space (510, 50) and a second space; a reinforcing wall containing a third sealing material having a third softening point that is higher than the first softening point, the reinforcing wall being adjacent to the peripheral wall in the internal space; an air passage connecting the first space (510, 50) and the second space together; and an evacuation port connecting the second space to an external environment, the evacuation step including evacuating the first space (510, 50) through the air passage, the second space, and the evacuation port, the sealing step including heating the partition to a temperature equal to or higher than the second softening point to deform the partition and thereby close the air passage, the method for manufacturing the glass panel unit further comprising a bonding step to be performed between the assembling step and the evacuation step, wherein the bonding step includes heating and once melting the peripheral wall at a melting temperature to hermetically bond the pair of glass substrates (200, 300) together with the peripheral wall, the melting temperature is set at a temperature equal to or higher than the first softening point and lower than the second softening point and the third softening point. the assembling step including providing a glass panel unit assembly, the glass panel unit assembly comprising: a pair of glass substrates (200, 300) arranged to face each other; a peripheral wall having a frame shape, containing a first sealing material having a first softening point and disposed between the pair of glass substrates (200, 300); a partition containing a second sealing material having a second softening point that is higher than the first softening point and partitioning an internal space, surrounded with the pair of glass substrates (200, 300) and the peripheral wall, into a first space (510, 50) and a second space; a reinforcing wall containing a third sealing material having a third softening point that is higher than the first softening point, the reinforcing wall being adjacent to the peripheral wall in the internal space; an air passage connecting the first space (510, 50) and the second space together; and an evacuation port connecting the second space to an external environment, the evacuation step including evacuating the first space (510, 50) through the air passage, the second space, and the evacuation port, the sealing step including heating the partition to a temperature equal to or higher than the second softening point to deform the partition and thereby close the air passage, the method for manufacturing the glass panel unit further comprising a bonding step to be performed between the assembling step and the evacuation step, wherein the bonding step includes heating and once melting the peripheral wall at a melting temperature to hermetically bond the pair of glass substrates (200, 300) together with the peripheral wall, the melting temperature is set at a temperature equal to or higher than the first softening point and lower than the second softening point and the third softening point. a pair of glass substrates (200, 300) arranged to face each other; a peripheral wall having a frame shape, containing a first sealing material having a first softening point and disposed between the pair of glass substrates (200, 300); a partition containing a second sealing material having a second softening point that is higher than the first softening point and partitioning an internal space, surrounded with the pair of glass substrates (200, 300) and the peripheral wall, into a first space (510, 50) and a second space; a reinforcing wall containing a third sealing material having a third softening point that is higher than the first softening point, the reinforcing wall being adjacent to the peripheral wall in the internal space; an air passage connecting the first space (510, 50) and the second space together; and an evacuation port connecting the second space to an external environment, the evacuation step including evacuating the first space (510, 50) through the air passage, the second space, and the evacuation port, the sealing step including heating the partition to a temperature equal to or higher than the second softening point to deform the partition and thereby close the air passage, the method for manufacturing the glass panel unit further comprising a bonding step to be performed between the assembling step and the evacuation step, wherein the bonding step includes heating and once melting the peripheral wall at a melting temperature to hermetically bond the pair of glass substrates (200, 300) together with the peripheral wall, the melting temperature is set at a temperature equal to or higher than the first softening point and lower than the second softening point and the third softening point.