An insulating plate for a secondary battery includes a wound electrode group, an electrolyte, a cylindrical battery case that houses the electrode group and the electrolyte, and a sealing body that seals an opening of the battery case and includes a discharge valve. The insulating plate is disposed between the electrode group and the sealing body and has a disk shape with a thickness T of 0.1 mm or more. The insulating plate has a first hole formed centrally therein and at least one second hole formed around the first hole so as to extend along the outer periphery of the disk shape. The ratio (=T/D) of the thickness T to a diameter D of the insulating plate is 0.016 or less, and the insulating plate has an opening ratio of 36% or less.