To eliminate such trouble that a user selects a wrong combination or forgets to hold one of a case main body and a complementary color plate by providing the case main body with the complementary color plate which has a ground color complementary to to the color of a marking tape and is pivoted rotatably on the case main body.

The complementary color plate 20 is constituted rotatably on a pivot 21 around the case main body 10. For an important item of a document, drawing, etc., to be memorized, a weak adhesive marking tape 5 is drawn out of the case main body 10 nd stuck on the object part, and a simple cutter 16 added to the case is processed to cut the tape. Then the complementary color plate 20 added to one surface of the case main body 10 is placed over the part where the weak adhesive marking tape 5 is stuck on the pivot 21 as a fulcrum, and then the corresponding part becomes dark black because of subtractive mixture of colors. Then this invisibility is utilized to increase memorization efficiency and confirm whether or not the object part has been memorized.