| Order: | Lord of Minakuchi Castle |
| Term Start: | 1585 |
| Term End: | 1600 |
| Natsuka Masaie | |
| Native Name: | 長束 正家 |
| Birth Date: | 1562 |
| Birth Place: | Owari Province |
| Death Date: | November 8, 1600 |
| Death Place: | Anraku-ji, Shiga Prefecture |
| Allegiance: | Niwa clan Oda clan Toyotomi clan Western Army |
| Battles: | Siege of Takamatsu (1582) Siege of Oshi (1590) Battle of Sekigahara (1600) |
| Rank: | Go-Bugyo |
| Commands: | Minakuchi Castle |
was a daimyō in the Azuchi-Momoyama period. He was served Niwa Nagahide and later Hideyoshi. He was one of the Go-Bugyō, or five commissioners, appointed by Toyotomi Hideyoshi.[1] [2]
He was born in Owari Province. Masaie served Niwa Nagahide who was a retainer of the Oda clan.[3] Later, because the domain of the Niwa clan was badly reduced after Hashiba Hideyoshi (Toyotomi Hideyoshi) ended the Sengoku period by reunifying Japan, Masaie served him and was given the rule of Minakuchi, Ōmi Province.
Hideyoshi congratulated Masaie on arithmetical faculty and appointed him as one of the Go-Bugyō, along with Ishida Mitsunari, Maeda Gen'i, Asano Nagamasa and Mashita Nagamori.
After Hideyoshi died, in 1600 Masaie and Ishida Mitsunari who was also one of the Go-Bugyō, put up Mōri Terumoto and raised their army against Tokugawa Ieyasu.
At the battle of Sekigahara, Masaie lined their army on Nangu-san with Mōri Hidemoto and Kikkawa Hiroie. However, Masaie was prevented from fighting by Hiroie and finally routed to Minakuchi. Setting fire to Minakuchi Castle, he committed suicide.His grave is at Anraku-ji, in Shiga Prefecture.