Hi Sakurai san,
I gave calfw a new try yesterday. It works well now and I really like it!
I tried to do, as you suggested, a export via htmlfontify-buffer.
It seems like it has problems with the cell alignment for those cells which contain an appointment.
Please see the attached picture (I can send you the html file in a private mail if you are interested to see the html code).
Could be the trouble of a non-monospace font, As far as I know Japanese fonts are monospace?
The generic htmlfontify-buffer might be a bit to simple. E.g. as you can see in the image, I use a dark colour scheme in emacs. This is also used in the export, making it difficult to print.
How about a real export function in calfw? Similar to what the calendar/diary offers.
I could help to work on a LaTeX template using graphical elements e.g. by using TikZ [1].
There are SVG-based generators and solutions written in python as well.
However, I have no idea how move the data of calfw into a template or into such a script.
My elisp knowledge is almost non existing.
All the best
Torsten