PURPOSE: To make the substrate maintenance work easier and eliminate adverse effects by electromagnetic wave on other substrates by installing cables only at the forefront portions in the pull-out direction of two neighboring substrates and also shielding these substrates.

CONSTITUTION: A power amplifier 1 includes four substrates 3a to 3d, and each of these substrates is separated and shielded by partitions 2a to 2c. In addition, substrates 30a and 30b are provided in opposition at both the sides of radiators 9a and 9b. Also, the substrates provided in opposition are respectively connected with cable 8. In addition, the connection between the substrates in opposition is made only by the cable wiring portions 7a and 7b, and each substrate is fixed by a plurality of screws 6. Neighboring substrates 3a and 30a and substrates 3b and 30b can be respectively pulled out in the direction of arrow Y with two substrates as one body. That is, two substrates connected by the cable 8 can be pulled out at the same time.