Copper alloy and copper alloy plate

Copper alloy of the present invention contains a 18～30Mass% of Zn, and 1～1.5Mass% of Ni, and 0.2～1Mass% of Sn, and 0.003～0.06Mass% of P, and , the balance being Cu and unavoidable impurities, 17 ≦ f1 = [Zn] + 5 × [Sn] -2 × [Ni] ≦ 30,14 ≦ f2 = [Zn] -0.5 × [Sn] -3 × [ Ni] ≦ 26,8 ≦ f3 = {f1 × (32-f1)} 1/2 × [Ni] ≦ 23,1.3 ≦ [Ni] + [Sn] ≦ 2.4,1.5 ≦ [Ni ] /〔Sn〕≦5.5,20≦〔Ni〕/〔P〕≦400 have a relationship, and has a metal structure which is α single phase.