A manufacturing method of a glass panel unit, comprising: a bonding step of hermetically bonding a first surface on one side in a thickness direction of a first substrate and a second surface on one side in a thickness direction of a second substrate together with a seal having a frame shaped, the first substrate including at least a glass pane, the second substrate including at least a glass pane; a pressure reduction step of reducing a pressure in an inside space surrounded by the first surface, the second surface, and the seal through an exhaust port formed in the first substrate or the second substrate to penetrate therethrough in the thickness direction; and a sealing step of sealing the exhaust port with a reduced pressure in the inside space being maintained, wherein in the sealing step, sealant disposed between the first surface and the second surface is deformed, and the sealant thus deformed seals an opening of the exhaust port, characterized in that: the sealant is higher in melting temperature than the seal, in the pressure reduction step, the sealant is disposed in the inside space and along the seal, the opening of the exhaust port is located at a space between the sealant and the seal, the seal and the sealant containing glass frit are disposed on the second surface of the second substrate, the sealant is located on an inner side of a corner section of the seal having a rectangular frame shape with the space from the seal, and the sealant is disposed in the vicinity of the opening of the exhaust port and adjacent to the seal. a bonding step of hermetically bonding a first surface on one side in a thickness direction of a first substrate and a second surface on one side in a thickness direction of a second substrate together with a seal having a frame shaped, the first substrate including at least a glass pane, the second substrate including at least a glass pane; a pressure reduction step of reducing a pressure in an inside space surrounded by the first surface, the second surface, and the seal through an exhaust port formed in the first substrate or the second substrate to penetrate therethrough in the thickness direction; and a sealing step of sealing the exhaust port with a reduced pressure in the inside space being maintained, wherein in the sealing step, sealant disposed between the first surface and the second surface is deformed, and the sealant thus deformed seals an opening of the exhaust port, characterized in that: the sealant is higher in melting temperature than the seal, in the pressure reduction step, the sealant is disposed in the inside space and along the seal, the opening of the exhaust port is located at a space between the sealant and the seal, the seal and the sealant containing glass frit are disposed on the second surface of the second substrate, the sealant is located on an inner side of a corner section of the seal having a rectangular frame shape with the space from the seal, and the sealant is disposed in the vicinity of the opening of the exhaust port and adjacent to the seal. the sealant is higher in melting temperature than the seal, in the pressure reduction step, the sealant is disposed in the inside space and along the seal, the opening of the exhaust port is located at a space between the sealant and the seal, the seal and the sealant containing glass frit are disposed on the second surface of the second substrate, the sealant is located on an inner side of a corner section of the seal having a rectangular frame shape with the space from the seal, and the sealant is disposed in the vicinity of the opening of the exhaust port and adjacent to the seal.