The signature on the tang reads:
備州長船勝光
Bishū Ōsafune Katsumitsu
It means "Katsumitsu of Ōsafune in the province of Bishū made this". Ōsafune was a famous sword-making region in Japan, located in where Okayama Prefecture is today. I think there were a few swordsmiths who used the name Katsumitsu, so it might be difficult to pinpoint which one is the Katsumitsu in these photos. Also, there are plenty of fakes around, and this sword could have had a fake name put on it centuries ago. Some pictures of the sword itself would help.