PURPOSE: To integrate a port selecting part and a frequency variable filter.

CONSTITUTION: A port selection circuit for connecting one of a first to an n-th ports P1 to Pn selectively to an (n+1)-th port Pn+1 is provided with n- pieces of switches of a first to an n-th switches SW1-1 to SWn-1 connected to the first to the n-th ports P1 to Pn at their one ends and connected to a common point at their other ends respectively. The frequency variable filter F to be set at a frequency characteristic to pass frequency assigned to the selected port in response to the selection of one of the first to the n-th ports P1 to Pn is connected between the common point and the (n+1)-th port Pn+1. The switches SW1-1 to SWn-1 and the frequency variable filter are integrated.