To provide an uranyl nitrate solution preparation device and an uranyl nitrate solution preparation method capable of promoting the dissolution of uranium oxide in nitric acid.

The means for solving the above problem is an uranyl nitrate solution preparation device, in an uranyl nitrate solution preparation device 1 comprising a preparation tank body 2 of preparing an uranyl nitrate solution from uranium oxide and nitric acid, provided with an inert gas feeding means 3 of feeding an inert gas from the side of the lower part 2G of the preparation tank body.