piercing hole of the ear holding portion 8b to form the middle ear portion 29 a holding member 31 provided with an eardrum 30 is inserted into the middle ear portion 29 of the ear holding portion 8b from the inside of the main body 2 in the assembling step of the model 1 the ear holding portion 8b of the ear portion 8 to which the holding member 31 with the eardrum 30 is fitted is inserted into the opening 15 of the combined front and back integuments 3a and 3b and the side opening 10 of the main body 2 aligned with each other as shown in fig1 and fig5 the diameter of the ear holding portion 8b is nearly equal to the diameter of the side opening 10 of the main body 2 accordingly the ear holding portion 8b is tightly fitted to the side opening 10 of the main body 2 since a flange 32 of the concha portion 8a contacts with the integuments 3a and 3b the ear holding portion 8b is restrained from being further inserted in operation for example the yieldable concha portion 8a is pulled backward by fingers substantially in the direction normal to the plane of the drawing accordingly the concha portion 8a is so deformed as shown by the dot dash line in fig5.