An indoor illuminating device includes at least one lamp and a housing. The at least one lamp includes a heat sink and a light emitting portion. The housing includes opposite top wall and bottom wall. The bottom wall defines at least one opening corresponding to the at least one lamp. The heat sink is received in the housing, and the light emitting portion of the at least lamp exposes out of the housing through the at least one opening. The housing further defines a first ventilation opening and a second ventilation opening. The heat sink of the at least one lamp is disposed in an airflow path between the first and second ventilation openings.