The present invention makes it possible to obtain a cross-flow fan blade with which it is possible to provide a cross-flow fan that is quiet and highly efficient even under heavy load. A leading edge portion (42) and a trailing edge portion (43) of a blade (40) are formed such that the radius (R1) of the leading edge portion (42) is larger than the radius (R2) of the trailing edge portion (43). A base portion (41) of the blade (40) has a maximum thickness (α) at a maximum thickness position (Mxp) which is closer to the leading edge portion (42) than the trailing edge portion (43), has a thickness (β) at a chord length intermediate position (CLm), and has a thickness (γ) at a position (CL5) that is only 5% of the chord length (CL) away from the outer peripheral edge (CLp) of the chord. The base portion (41) is formed such that the value obtained by dividing thickness (β) by maximum thickness (α) is larger than the value obtained by dividing thickness (γ) by thickness (β).
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