NOVELTY - An epoxy resin hardener comprises non-modified polyamino compound having two or more amino groups in a molecule and active hydrogen derived from amino group, and phenethyl-ized polyamino compound (I). The phenethyl-ized polyamino compound is obtained by addition reaction of styrene and polyamino compound (II).    USE - Epoxy resin hardener is used for epoxy resin composition for epoxy resin-hardened material and manufacture of blade (all claimed) for offshore wind power generation. Uses include but are not limited to molded material for large-sized component for ship and aircraft, coating material, adhesive agent, decoration material, paint raw material, and hardening agent of thermosetting resin composition used for fiber-reinforced plastic molded product.    ADVANTAGE - The epoxy resin hardener is in low-viscosity liquid state under normal temperature of 30 degrees C. The blade economically manufactured using the epoxy resin composition containing epoxy resin hardener has excellent durability. The epoxy resin-hardened material economically manufactured using the epoxy resin composition containing epoxy resin hardener has excellent mechanical characteristics.    DETAILED DESCRIPTION - An epoxy resin hardener is obtained by non-modified polyamino compound having two or more amino groups in a molecule and active hydrogen derived from amino group, and phenethyl-ized polyamino compound of formula (I). The phenethyl-ized polyamino compound is obtained by addition reaction of styrene and polyamino compound of formula: H2N-H2C-W'-CH2-NH2 (II).    W'=phenylene or cyclohexylene;and    At least R1,R2,R3=H, and remaining are phenethyl.    INDEPENDENT CLAIMS are included for the following:    (1) epoxy resin composition, which contains epoxy resin hardener and epoxy resin;    (2) epoxy resin-hardened material, which is obtained by hardening the epoxy resin composition;    (3) blade for wind power generation, which is obtained by hardening the epoxy resin composition; and    (4) manufacture of blade for wind power generation, which involves molding epoxy resin composition and reinforced fiber by infusion molding method or prepreg molding method.