An indoor unit of a refrigeration apparatus includes: a drain pan that includes four wall surfaces including a first wall surface, and has a quadrangle shape in a plan view; a heat exchanger disposed above the drain pan and through which a combustible refrigerant, having a larger specific gravity than air, flows; a fan that generates air flow to the heat exchanger; a gas sensor that detects a refrigerant leakage; and a casing accommodating the drain pan, the heat exchanger, the fan, and the gas sensor.