An axial-flow fan has a plurality of main fins (702), and auxiliary fins (703) provided between the main fins (702), where the position of a front end of the auxiliary fin (703) relative to X axis and the position of a front end of the main fin (702) adjoining the auxiliary fin in reverse-rotary direction are aligned, the height of the auxiliary fin (703) is approximately three fourths of the height of the main fin (702), and the cross sections of the main fin (702) and the auxiliary fin (703) taken along the axial direction of the main shaft are streamlined.