This is a very nice kozuka by Goto Mitsuyoshi. Goto Mitsuyoshi, also known as Shinjo, was the fifteenth mainline master for the Goto family. His art name was Goto Shinjo. He was the first son of the fourteenth master, Goto Keijo. Mitsuyoshi was born in Edo on February 16, 1780 and he died on June 7, 1843. He had four sons and three daughters.
In April of 1804 he succeeded his father, Goto Keijo and became the fifteenth master of the mainline Goto family. On June 3 he adopted the name Shirobei, and he received a stipend of 250 koku. In July of 1835 he retired as head of the family after 31 years.
There are many pieces of his work extant. Additionally, he was prolific in doing attributions on the works of former Goto masters. Thus we find his attribution signature on many mumei pieces done by prior generations.
I have not as yet submitted it for papers. I have owned enough pieces by him over the years that I would be amazed if this piece is not genuine.