A signal transmission device includes: an input signal conductor in which an input signal current flows and thereby generating an input signal magnetic field; a magnetically-biasing conductor in which a biasing current flows and thereby generating a biasing magnetic field; and one or more magnetoresistive elements in each of which a sensing current flows and thereby generating a self-biasing magnetic field, and each including a magnetization free layer having a magnetization direction which varies in response to the input signal magnetic field, the biasing magnetic field, and the self-biasing magnetic field. Each of the biasing magnetic field and the self-biasing magnetic field is applied to the magnetization free layer in a same direction to each other.