To provide structure capable of easily attaching/detaching an information storage device without requiring any screw at the time of fixing the storage device on a casing for a portable information processor.

Buffer members 2 are fitted to positioning parts 1b of the casing 1, an information storage device 4 is fitted on the buffer members 2 while fitting the members 2 to the positioning parts 1b and a press board 5 is put on the device 4 by inserting projection parts 5a formed one side of the board 5 into locking parts 1d formed on cylindrical parts 1a formed integrally with the casing 1 and inserting projection parts 5a formed on the other side of the board 5 into locking parts 1d while utilizing the elasticity of the cylindrical parts la to fix the device 4.