A microstrip resonator including a dielectric substrate, a resonance electrode on a first main surface of the dielectric substrate, and a ground electrode over an entire second main surface of the dielectric substrate. The resonance electrode includes a superconducting film and a metal film deposited in that order. The ground electrode includes a superconducting film and a metal film deposited in that order. The superconducting film functions as an electrode in low-temperature operation below a critical temperature, and the metal film functions as an electrode in high-temperature operation at or above the critical temperature. The length of the superconducting film of the resonance electrode is set to be longer than that of the metal film of the resonance electrode, so that the resonance frequency in low-temperature operation is substantially equal to the resonance frequency in high-temperature operation.