To make a cup of coffee by pouring hot water just once by providing a coffee maker of simple drip type whose paired opposite side plates have bent back pieces continuous to the upper edges thereof so as to be bendable, and bend lines formed from the respective corners of bottom board toward the upper edges of the bent back pieces.

A blank has a square bottom plate 11 whose one side is larger than the dia. of a cup 1, and four side plates 12, 13 being continuous so as to be bendable with the four sides (a) being bend lines. At the central part of the bottom plate 11 a circular opening 11a is formed. Among the side plates 12, 13, those opposite to each other through the bottom plate 11 have the same shape. Between the paired side plates 12, 13 adjacent to each other, a continuous piece 14 is provided. To upper edges (e) of the paired opposite side plates 12, bent back pieces 15 are continoutly provided so as to be bendable with the upper edges (e). On the paired side plates 12 bend lines (f) are provided which extend from respective corners of the bottom plate 11 to the upper edges (e) of the bent back pieces 15.