An object of the present invention is to provide a terahertz oscillator that does not have an MIM capacitor structure of which producing is intricacy, and oscillates due to resonance of an RTD and stabilizing resistors. The present invention is a terahertz oscillator, wherein a slot antenna having a slot is formed between a first electrode plate and a second electrode plate which are applied a bias voltage, stabilizing resistors to respectively connect to the first electrode plate and the second electrode plate are provided in the slot, an RTD is provided on the second electrode plate through a mesa, and a conductive material member to form an air bridge between the first electrode plate and the mesa is provided, and wherein an oscillation in a terahertz frequency band is obtained due to a resonance of the RTD and the stabilizing resistors.