This is a puzzle game that is often called "[Nanba-pure-su] ([nanpure])" in general in Japan.

It is a standard game with which it is called Sudoku in countries other than Japan and is widely familiar.
Rule
Either of figure of 1?9 is put in the mass that has become empty.
The same figure in the block of 3×3 enclosed in each row and the heavy line on length and side disregards and plurals do not disregard it yep.

VerUp! The difficulty setting was added.

1.8 Bug fix.