An outdoor unit 1 of an air-conditioning apparatus includes a housing having a box shape and including air inlets formed on side surfaces and an air outlet formed on an upper surface, a fan provided to an upper side in the housing and configured to discharge, through the air outlet, outside air sucked through the air inlets, and a heat exchanger provided in the housing along each of the air inlets. The heat exchanger includes an upper heat exchanger disposed at an upper part of the housing and a lower heat exchanger disposed at a lower part of the housing. In plan view, the housing has different widths in short-side and long-side directions, and the width in the short-side direction at the upper part of the housing is longer than the width in the short-side direction at the lower part of the housing.