Inserting Japanese characters into UTF-8 MySQL database via php

[marcin]

I have problems with inserting Japanese chars into MySQL database. This
operation results in two completetely different strings that I can see
via phpMyAdmin:
$word: SELECT word FROM table;
INSERT $word INTO table;

Both commands are executed direclty via PHP, phpMyAdmin shows the
original word (inserted into table via phpMyAdmin) correctly and a
wrong copy (f.e. %&c/#....) of word inserted via PHP.

I preasume that the problem is PHP default coding, I tried to convert
encoding to UTF-8 by mb_convert_encoding($key, "UTF-8", "auto"); with
no success.