To provide a device and a method for producing nanoparticles effectively and at low cost without using an organic solvent at all in the production process.

A device for producing nanoparticles (ultrasonic rotary nano-homogenizer) includes a horn 5 rotating while ultrasonically vibrating, and an ultrasonic rotary unit 1 configured such that the ultrasonic vibration and rotation movement are applied to the horn 5. The horn 5 is put in a solution 6 having a raw material of the nanoparticles as a solute and the horn 5 is rotated while ultrasonic vibration is given to the solution 6 to produce the nanoparticles.