Koshonin is in kosho yakuba.
He is a government official and has the experience of 30 years as a judge of a court.
He can make the document that has the same effect of the judicial decision.

You pay attention that he does not conduct notary of your passport copy by a photocopier.
You post the items in your passport on a sheet of paper and take an oath that it has same letters from your passport by yourself.
Koshonin notarizes your written oath.
This procedure for certificate is legally correct in Japan.
But the other party who receive the document may not accept it unfortunately.
The other party may not request it and you had better make sure that this document of koshonin is acceptable or not acceptable in advance.