A heat exchanger having a plurality of heat-transfer tubes arrayed at intervals in vertical and anteroposterior directions and arranged so that an equilateral triangle is formed by lines connecting the centers of heat-transfer tubes located vertically and anteroposteriorly adjacent to each other; and a plurality of heat-transfer corrugated fins arranged at intervals in an axial direction of the heat-transfer tubes, characterized in that when an external diameter of each of the heat-transfer tubes is V1; a vertical pitch of the heat-transfer tubes is V2, a fin pitch of the heat-transfer corrugated fins is V3, a fin plate thickness of each of the heat-transfer corrugated fins is V4, and a corrugate height of the heat-transfer corrugated fins is V5, any one of V2, V3 and V5 is set within a given range.