Provided is a mixing device that is configured to install therein a multi-well plate including a plurality of wells capable of containing matter to be mixed and includes mixing mechanisms each of which mixes the matter to be mixed with a motor and is provided for each of the wells. The mixing mechanisms each includes a first rotator that is connected to the motor and rotates due to activation of the motor, a mixing rod that mixes the matter to be mixed, a second rotator that supports the mixing rod, a magnetic coupling mechanism that magnetically couples the first rotator to the second rotator, and a seal ring that surrounds an opening of the well and is capable of closing the well together with the second rotator.