the case of fig3 c the lower portion of the circumferential wall portion 3 b of the upper shell 3 is folded back outwardly and forms a folded back portion 19 the circumferential wall portion 4 b of the lower shell 4 has a step portion 4 d which receives the lower end of the folded back portion 19 to regulate the spacing between the upper and lower shells 3 4 and the upper end portion of the circumferential wall portion 4 b of the lower shell 4 is bend inwardly as a caulking portion 20 and caulked onto the folded back portion 19 of the upper shell 3 whereby the housing is assembled referring to fig4 there is shown a disk cartridge constructed in accordance with a third embodiment of the present invention this embodiment is characterized in that upper and lower shells 3 4 are formed by folding and caulking a single metal plate 21 that is at approximately the longitudinal center position of the metal plate 21 a protrusion 21 a is formed so it extends perpendicular to the longitudinal direction of the metal plate 21 and by folding back the metal plate 21 along the protrusion 21 a the left side plate portion 21 b of the protrusion 21 a forms the flat plate portion of the upper shell 3 while the right.