I can't read the first line except for the last two kanji: Middle School:
The second line is his name, Mizunuma Yōichi:
Hi Visor-san, Guy-san,
The characters are:
宇和島城南中学校 (Uwajima-Jyou Nann Chuu-Gakkou) - Uwajima Castle South Hight School.
Uwajima Castle - Wikipedia, the free encyclopedia
This school was built on a former IJN Yokaren (vounteer pilot training) Base, started in 1947.
Oops, my mistake.
So why would this be written on the canteen ?
Maybe used by a teacher or a student post war.
'Little Citizens' and 'Star Pupils': Military Middle Schools in Wartime Japan :: JapanFocus
There is a picture with uwajima middle school mentioned. Says gun training 1936. Is this the same uwajima middle school mentioned on the canteen?
I think that is one of the middle school in Uwajima.
Not necessary the one written on the canteen.