In the upper part and the lower part of a micro-nano bubble generation section 34 in a micro-nano bubble bathtub 1, two kinds of micro-nano bubbles different in a size distribution are generated by first and second micro-nano bubble generators (submerged pump-type micro-nano bubble generator 2 and spiral flow-type micro-nano bubble generator 10) of two kinds, so that bathtub water containing micro-nano bubbles in a wide size distribution can be produced in a large amount. Some of the water containing micro-nano bubbles generated in the lower part is thrown into the first micro-nano bubble generator (spiral flow-type micro-nano bubble generator 10) in the upper part, so that the spiral flow-type micro-nano bubble generator 10 can generate micro-nano bubbles in a smaller size. Therefore, in this bathtub, micro-nano bubbles abundant in size and large in amount can be produced economically.