A substrate gap adjusting device adjusts a gap between first and second substrates in a composite substrate. In the substrate gap adjusting device, the composite substrate includes the first substrate; the second substrate that is oppositely bonded to the first substrate through a sealant, the second substrate having a smaller area than the first substrate; and liquid crystal that is injected into a space surrounded by the first substrate, the second substrate, and the sealant. The substrate gap adjusting device includes a first base that has a mounting section; a ring-shaped support member that is mounted on the mounting section and that comes in contact with a second surface out of two surfaces of the first substrate so as to support the composite substrate, the second surface being opposite to a first surface on which the second substrate is bonded; a substrate pressing section that has a movable range in a normal direction of a plane defined by the support member and comes in contact with the first substrate at a circumferential edge of the first surface in any position of the movable range; and an external applying section that transmits a force to the substrate pressing section, the force displacing the substrate pressing section within the movable range. In this structure, the circumferential edge is positioned at the outer side of the support member, as seen from the normal direction.