PURPOSE: To retain high acoustic quality while saving materials and simplifying manufacturing processes by performing joining of a baffle plate and the side face of a cabinet by forming an inner frame made by compression forming of wood chips mixed with a bonding agent in one body.

CONSTITUTION: A bonding agent is coated on the side face of a box frame 1, and the box frame 1 is set in the receiving concavity 9 of a lower die 8. Then, a specified quantity of wood chips 22 mixed with the bonding agent are put in the box frame 1, and at the same time, the lower die 8 is heated to 120∼170°C. The bonding agent of urea group, melamine group, phenol group etc. is used. Then, an upper die 18 is lowered, and wood chips 22 in the box frame 1 are pressed by pressure of 20∼50kg/cm2. Consequently, pistons 13a, 13b move downward, and a baffle plate 12 having window holes 13a, 13b for loudspeaker provided with peripheral grooves 16a, 16b and an inner frame 20 thermally compressed in the space between the outer peripheral face of the upper die 18 and inner side face of the box frame 1 and joined on the inner side face and corner blocks 21 formed in a block.