It is called a mouth organ. It is a small wind instrument, mostly with 32 and 37 keys. The mouth is used as the source of wind (just like the organ used in the music teacher's class when I was a child, which uses pedals as the source of wind). The same), played on the keyboard. It is actually a "mouth organ", so it is called a mouth organ. It is cheap and relatively easy to learn compared to other instruments. Therefore, it is now more popular to be used in music classes in primary and secondary schools.

You can buy a copy of "Easy Introduction to Learning the Mouth Organ from Scratch" from China Drama Publishing House. That book is good