To realize the fairly closing of a pocketbook without bringing pen holders into contact with each other by a method wherein a pen is inserted in a space made between a sheet anglewise swollen along rings, which is formed by inserting the rings in respective mounting holes provided at both the ends of the square sheet, and a fitment.

At both the ends of a square sheet 1, mounting holes 2 having the diameter of about 5mm are provided at least two symmetrical positions. At the use of the sheet, the rings 5, each of which has a ring diameter of 17mm or more, of the fitment 4 of a system pocketbook 3 are opened so as to be inserted in the mounting holes 2 at both the ends of the sheet 1. By closing the ring 5, the sheet 1 swells anglewise along the rings 5 so as to produce a space between the sheet and the fitment. By inserting a pen in the space and pinching the pen with a pen grip to the sheet 1, the pen is tightly fixed. Since the sheet 1 serving as the pen holder at the first part of a pocketbook, the pocketbook can fairly be closed.