An object of the invention is to change over accurately the switch part between use condition and nonuse condition. A signal transmitting and receiving circuit 100 for transmitting and receiving signals comprises a tuning and matching circuit 3 for transmitting and receiving the signals, a signal communication wire 4 transmitting the signals, and a wavelength wire 11 having a length (L) defined by a relational expression given in an Equation of L=N(.lamda./4) where L: length of the wavelength wire, N: 1, 2, 3, . . . , and .lamda.: wavelength. The circuit 100 also comprises a switch part 12 changing over between a grounded connection target and an ungrounded connection target. Further, the tuning and matching circuit 100 is mutually connected to the signal communication wire 11, and the wavelength wire 11 is constituted such that one end thereof is connected between the tuning and matching circuit 3 and the signal communication wire 4, and the other end thereof is connected to the switch part 12.