A sheet storage apparatus (for example, a banknote storage mechanism 32) includes an entering unit (for example, a pushing unit 46) configured to enter into a storage bag (for example, a banknote storage bag 34) supported by a supporter (for example, holding members 36) and a controller 80 configured to control the driving unit (for example, a motor 54) for driving the entering unit. The controller 80 controls the driving unit such that the entering unit enters into the storage bag supported by the supporter and comes in contact with the sheet stored in the storage bag to detect an upper end position of the sheet stored in the storage bag.