Also called "semi-voiced sound mark".

A Japanese diacritical mark used with hiragana or katakana. It changes the sound of the kana as follows:

Without handakuten:  ha hi fu he ho
   With handakuten:  pa pi pu pe po

It can only be used on the kana listed above.

The handakuten looks like a small circle placed to the upper right of the kana. In small print, it is easily confused with dakuten.

See also dakuten.