I searched with picture to Google, and they suggest it might be
I also went through the list of insects from this page, http://www7a.biglobe.ne.jp/~yabuyama/koucyuumoku.html, it is in Japanese. The bug that looked like the one in picture the most was a ベニカミキリ (latin name: Purpuricenus temminckii), but it did not have the black dots, and it seems too small.
The insect was found near a pond in a Japanese garden in Fukuoka, Kyushu in June. I do not recall the size of it, but I think it was somewhere between 1cm and 3cm long.