A manufacturing method of a glass panel unit of the present invention includes a bonding step, a pressure reduction step, and a sealing step. In the bonding step, a first substrate and a second substrate are hermetically bonded together with a seal having a frame shape. In the pressure reduction step, a pressure in an inside space formed between the first substrate and the second substrate is reduced through an exhaust port. In the sealing step, sealant melted is dropped toward the exhaust port, thereby sealing the exhaust port with the sealant.