Nowadays, various mobile communication systems are put to practical use along with the advancement of radio communication technologies.  For example, mobile communication systems compliant with schemes such as PDC, CDMA and PHS are put to practical use in Japan. 
Along with the practical use of various mobile communication systems, multiband radio communication devices (such as cellular phone terminals) supporting multiple frequency bands (multiband) have been provided.  Specifically, a multiband radio communication device is capable of transmitting and receiving simultaneously multiple radio signals in different frequency bands. 
In a multiband radio communication device, in order to prevent a radio signal in a certain frequency band from entering, as noise, into a receiver circuit for receiving a radio signal in a different frequency band, a filter that suppresses the noise is provided in general (refer to Japanese Patent Application Publication No.  Hei 11-112382 (pages 4 to 5 and FIG.  1) for example).