Sheet stack apparatus and sheet stacking method

A sheet stack apparatus comprising:

• a storage portion configured to support sheets conveyed one by one in a standing position;
• a receiving portion configured to receive lower ends of the sheets supported by the storage portion;
• an assisting member configured to move between a first position where the assisting member is separated from the storage portion and a second position where the assisting member contacts with the sheets conveyed to the storage portion, and to assist stacking of the sheets on the storage portion;
• and
• a holding member configured to move in correspondence with a movement of the assisting member via an attaching portion, the holding member separating from the lower ends of the sheets when the assisting member is at the second position, and the holding member contacting with the lower ends of the sheets when the assisting member is at the first position, the holding member including a flexible first paddle attached to the assisting member via the attaching portion and a second paddle provided on a leading edge side of the first paddle, the second paddle having an end part on a side of the attaching portion that is provided removably on the first paddle to contact with the lower ends of the sheets supported by the storage portion.