A glass panel unit manufacturing method, comprising: a seal applying step of applying a seal in a frame shape onto a periphery part of either or both of a first surface of a first substrate and a second surface of a second substrate, the first substrate including at least a glass plate, the second substrate including at least a glass plate, the first surface being one surface in a thickness direction of the first substrate, and the second surface being one surface in a thickness direction of the second substrate; a getter applying step of applying a getter onto the second surface of the second substrate; a pillar mounting step of mounting a pillar onto the second surface of the second substrate; a bonding step of hermetically bonding, with the seal, the first surface of the first substrate and the second surface of the second substrate to form an inner space surrounded with the first surface, the second surface and the seal other than an exhaust path capable of exhausting gas to an outside, such that the first surface and the second surface face each other with a prescribed interval; a pressure reducing step of reducing a pressure in the inner space; and a sealing step of sealing the inner space while maintaining a reduced pressure in the inner space, the bonding step being performed after the seal applying step, the getter applying step and the pillar mounting step, in the bonding step, the first substrate and the second substrate being set with sandwiching the seal and the pillars, and heated in the sealing furnace, the seal including a protruding portion, positioned outside of edges of the first surface of the first substrate and the second surface of the second substrate, in a state where the inner space has been formed, and the protruding portion having a length, along the thickness directions of the first substrate and the second substrate, longer than the prescribed interval. a seal applying step of applying a seal in a frame shape onto a periphery part of either or both of a first surface of a first substrate and a second surface of a second substrate, the first substrate including at least a glass plate, the second substrate including at least a glass plate, the first surface being one surface in a thickness direction of the first substrate, and the second surface being one surface in a thickness direction of the second substrate; a getter applying step of applying a getter onto the second surface of the second substrate; a pillar mounting step of mounting a pillar onto the second surface of the second substrate; a bonding step of hermetically bonding, with the seal, the first surface of the first substrate and the second surface of the second substrate to form an inner space surrounded with the first surface, the second surface and the seal other than an exhaust path capable of exhausting gas to an outside, such that the first surface and the second surface face each other with a prescribed interval; a pressure reducing step of reducing a pressure in the inner space; and a sealing step of sealing the inner space while maintaining a reduced pressure in the inner space, the bonding step being performed after the seal applying step, the getter applying step and the pillar mounting step, in the bonding step, the first substrate and the second substrate being set with sandwiching the seal and the pillars, and heated in the sealing furnace, the seal including a protruding portion, positioned outside of edges of the first surface of the first substrate and the second surface of the second substrate, in a state where the inner space has been formed, and the protruding portion having a length, along the thickness directions of the first substrate and the second substrate, longer than the prescribed interval.