An acoustic echo canceller apparatus for canceling an echo signal input to a microphone in a mobile terminal. The under cover has a pair of right and left cover members detachably connected together along opposing vertical edges thereof; an opening formed in at least one of the cover members for allowing access to the engine. Subsequently, the metal sheet is press-bent along two longitudinal lines, passing respectively through the cut portions 30, so that the opposite right and left side wall plates 20R and 20L, having the opposed press-connecting blades 22R and 22L, respectively, are formed upright respectively at the opposite side edges of a bottom wall plate 18. The opening has a width which prevents the head of the fastener from passing therethrough. The dendritic cells derive from this method have all the features of mature cells.