A signal transmitter prevented from outputting an unwanted signal to the outside, which is generated at the time of changing any of various setting parameters such as a channel through which a signal is to be transmitted and the degree of modulation of an intermediate frequency signal to be supplied without deteriorating impedance matching between circuits. This signal transmitter has a local oscillator for outputting a local oscillation signal; a mixer for mixing a supplied television intermediate frequency signal with the local oscillation signal and frequency-converting the resultant signal to a television signal of a specific channel through which the signal is to be transmitted among television channels; and a variable band-pass filter connected at a post stage of the mixer and tuned to the frequency of the specific channel. The tuning frequency of the variable band-pass filter can be shifted out of the frequency band of the specific channel.