A 23-meter-tall pile driver fell over Thursday in Yachiyo, Chiba Prefecture, smashing part of a house, police said.
The top of the 60-ton machine crashed through the roof of the home and came to rest in the ground-floor living room of the two-story structure.
Shizuko Ota, 76, was in the kitchen and escaped injury, the police said.
The pile driver was being used to dismantle an old hospital across the street.
The ground at the construction site was reportedly muddy from rain that had fallen earlier, but the machine tipped over as it was being moved on a steel plate laid out on the ground, the police said.
The machine was being used to pull posts out from the basement of the hospital.
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