Toomizuka Kofun in Wakabayashi-ku, Sendai City, Miyagi Prefecture, is a keyhole-shaped kofun built from the end of 4th century to the early 5th century. With a total length of 110 m and a height of 6.5 m, it is the 5th largest kofun in the Tohoku region. It is designated as a Historic Site by the national government.

The characteristic of this keyhole-shaped kofun is that the square front part is extremely lower than the round rear part. The kofun is surrounded with an irregular-shaped moat, which is about 10 to 40 m wide. The number of burial accessories is extremely small for the size of the kofun. Only 1 quartz cylindrical jewel, 4 glass balls and 18 combs made of lacquered bamboo were excavated.

The half of the round rear part was destroyed when the U.S. Air Force expanded its Kasumime Air Base. The kofun site is converted into a park now. The excavated articles are preserved and displayed at Sendai City Museum.