Provided are a polyurethane and a curable composition capable of obtaining an overcoat film for a flexible wiring board that is excellent in low-warpage properties, flexibility, long-term insulation reliability, and wiring disconnection preventing properties. The polyurethane has: a structural unit of formula (1) (in formula (1), an n-number of R1 each independently represents a 1,2-phenylene group or a 1,2-phenylene group having a substituent, an (n+1)-number of R2 each independently represents a hydrocarbon group having 3-9 carbon atoms, and n represents an integer from 1 to 50); a structural unit of formula (2) (in formula (2). R3 represents a divalent organic group having 6-14 carbon atoms); and a structural unit of formula (3) (in formula (3), R3 represents a divalent organic group having 6-14 carbon atoms, and R4 represents a methyl or ethyl group).