Yes, I don't think this is an official number though. It is almost sufficient (according to specialized lawyers) on its own but not absolutely necessary depending on the person degree, skills and plenty of other things.

edit: After checking a relevant Japan ministry of justice webpage [1], 5m yen is given as an indicator, which is why I suppose it is the value given by most lawyers.

[1]: http://www.moj.go.jp/nyuukokukanri/kouhou/nyukan_nyukan20.ht...