Midono Dam, Arch dam on the Azusa River in Matsumoto, Nagano Prefecture, Japan.

Midono Dam is a 95.5-metre arch dam on the Azusa River in Matsumoto, Nagano Prefecture. It stands at the confluence of the Azusa and the Midono River, between the upstream Nakanoto Dam and the downstream Inekoki Dam, and its reservoir serves as the lower pond for the Azumi Power Station.

This dam was completed in 1969 during Japan's period of rapid infrastructure growth and became part of a broader effort to develop water resources in the Nagano area. Its construction reflected the nation's rising need for electricity after World War II.

The dam sits at the confluence of the Azusa and Midono rivers, and the reservoir behind it, the Midono Chōseichi, serves as the lower pond for the Azumino Power Station just below Nakanawado Dam. Midono Dam itself is the upper pond for pumped storage using the Inekoki reservoir downstream, a rare arrangement in Japan. The dam crest is a walkway, and from the left bank a tunnel leads to the upper Midono River, where anglers fish for iwana char.

The dam sits in Nagano's mountain region and requires planning to reach from major cities, as it is located in a remote area. A visit works best during daylight hours when you can see the full structure and the surrounding valley clearly.

Midono Dam is one of the few dams in Japan serving as both upper and lower reservoir in pumped storage: its own lake feeds the 245,000 kW Midono Power Station below, while the same lake is the lower pool for the Azumi Power Station at Nakanoto Dam upstream. Its spillway is a ski-jump type on the right bank, chosen because the power station sits directly below the dam.