A blade of a cross-flow fan comprising: a leading-edge portion arranged on the inner-peripheral side of the cross-flow fan, the leading-edge portion being formed in an arc-like shape; a trailing-edge portion arranged in the outer-peripheral side of the cross-flow fan, the trailing-edge portion being formed in an arc-like shape; and a base portion formed between the leading-edge portion and the trailing-edge portion, the base portion having a pressure surface configured and arranged to generate positive pressure, and a suction surface configured and arranged to generate negative pressure; the leading-edge portion and the trailing-edge portion being formed such that the radius of the leading-edge portion is greater than the radius of the trailing-edge portion; wherein the pressure surface and suction surface of the blade are curved so as to describe smooth arcs that expand toward the outer-peripheral side in cross-section; wherein the distance between the pressure surface and the suction surface gradually varies from the inner-peripheral side toward the outer-peripheral side; and the base portion being formed so as to have a maximum thickness at a position of maximum thickness, a first thickness at an intermediate position on a blade chord, and a second thickness at a position set apart from an outer-peripheral end of the blade chord by 5% of the chord length; wherein the base portion is configured such that the position of maximum thickness is positioned within a range of 5-45% of the chord length from an inner-peripheral end; and wherein the base portion is configured such that the value of the ratio between the value obtained by dividing the second thickness by the first thickness and the value obtained by dividing the first thickness by the maximum thickness is set to 0.85 or less. a leading-edge portion arranged on the inner-peripheral side of the cross-flow fan, the leading-edge portion being formed in an arc-like shape; a trailing-edge portion arranged in the outer-peripheral side of the cross-flow fan, the trailing-edge portion being formed in an arc-like shape; and a base portion formed between the leading-edge portion and the trailing-edge portion, the base portion having a pressure surface configured and arranged to generate positive pressure, and a suction surface configured and arranged to generate negative pressure; the leading-edge portion and the trailing-edge portion being formed such that the radius of the leading-edge portion is greater than the radius of the trailing-edge portion; wherein the pressure surface and suction surface of the blade are curved so as to describe smooth arcs that expand toward the outer-peripheral side in cross-section; wherein the distance between the pressure surface and the suction surface gradually varies from the inner-peripheral side toward the outer-peripheral side; and the base portion being formed so as to have a maximum thickness at a position of maximum thickness, a first thickness at an intermediate position on a blade chord, and a second thickness at a position set apart from an outer-peripheral end of the blade chord by 5% of the chord length; wherein the base portion is configured such that the position of maximum thickness is positioned within a range of 5-45% of the chord length from an inner-peripheral end; and the base portion is configured such that the value of the ratio between the value obtained by dividing the second thickness by the first thickness and the value obtained by dividing the first thickness by the maximum thickness is set to 0.85 or less.