A measurement device includes a microwave generator, an electron spin resonance member, and an observation system. The microwave generator is configured to generate a microwave. The microwave is configured for an electron spin quantum operation based on a Rabi oscillation. The microwave generator has a coil configured to emit the microwave and an electrostatic capacitor electrically connected in parallel to the coil. The microwave is irradiated to the electron spin resonance member. The observation system is configured to measure a physical quantity in a measured field in response to a state of the electron spin resonance member when the electron spin resonance member is irradiated by the microwave. The coil has first and second ends from which first and second legs continuously extended. The electrostatic capacitor spans the first and second legs and is electrically connected in parallel to the coil.