A mold platen includes a mold plate to which a mold is attached, a rear-surface plate provided opposite to the mold plate, coupling portions configured to be coupled to respective tie rods at four corners of the mold plate and the rear-surface plate, a cylindrical rib that is provided between the mold plate and the rear-surface plate and is located at a center part of the mold plate and the rear-surface plate, a diagonal reinforcing rib that is provided between the mold plate and the rear-surface plate and is configured to connect the cylindrical rib and each of the coupling portions, and a longitudinal/lateral reinforcing rib that is provided between the mold plate and the rear-surface plate and extends from the cylindrical rib along a position between the adjacent coupling portions.