A Cu-Ni-Si-based copper alloy plate comprising: 1.0 mass% to 3.0 mass% of Ni; 0.2 mass% to 0.8 mass% of Sn; 0.3 mass% to 1.5 mass% of Zn; 0.001 mass% to 0.2 mass% of Mg Si at a concentration of 1/6 to 1/4 of a mass% concentration of Ni; and optionally, further comprising one or two of: Fe: 0.007 mass% to 0.25 mass%; P: 0.001 mass% to 0.2 mass%; C: 0.0001 mass% to 0.001 mass%; Cr: 0.001 mass% to 0.3 mass%; and Zr: 0.001 mass% to 0.3 mass%, with a remainder of Cu and inevitable impurities, wherein, an average value of aspect ratios (a minor axis of crystal grains/a major axis of crystal grains) of each crystal grains in the alloy structure is 0.4 to 0.6, an average value of grain orientation spread in all crystal grains, which is measured through an EBSD method using a scanning electron microscope equipped with an electron backscatter diffraction image system, is 1.2° to 1.5°, and a ratio (Lσ/L) of a total special grain boundary length Lσ of special grain boundaries to a total grain boundary length L of crystal grain boundaries is 60% to 70%, the total special grain boundary length Lσ of special grain boundaries to a total grain boundary length L of crystal grain boundaries being measured thanks to a pretreatment, in which a 10 mm * 10 mm specimen is immersed in 10% sulfuric acid for ten minutes, then washed using water, water is scattered through air blowing, and then a surface treatment was carried out on the water-scattered specimen using a flat milling apparatus at an acceleration voltage of 5 kV and an incidence angle of 5° for one hour of exposure time, next, the surface of the specimen was observed using a scanning electron microscope, the observation conditions being an acceleration voltage of 25 kV and a measurement area of 150 μm * 150 μm, the orientations of all pixels in said measurement area range being measured at a step size of 0.5 μm, and a boundary for which the orientation difference between adjacent pixels is 5° or more being defined as the crystal grain boundary, the spring bending elastic limit is 450 N/mm 2 to 600 N/mm 2, the solder resistance to heat separation is favorable and deep drawing workability is excellent at 150°C for 1000 hours, said solder resistance to heat separation being measured by cutting a specimen into a strip shape having a width of 10 mm and a length of 50 mm, then immersing the specimen in 60%Sn-40%Pb solder at 230°C+-5°C for 5 seconds, 25% rosin ethanol being used as a flux, then heating the obtained material at 150°C for 1000 hours, bending it 90° at a same bending radius as a plate thickness, returning it to the original angle, and visually observing a presence of solder detachment at bent portions, and said deep drawing workability being obtained by cups manufactured using a tester under conditions of a punch diameter of 10 mm and a lubricant being grease. 1.0 mass% to 3.0 mass% of Ni; 0.2 mass% to 0.8 mass% of Sn; 0.3 mass% to 1.5 mass% of Zn; 0.001 mass% to 0.2 mass% of Mg Si at a concentration of 1/6 to 1/4 of a mass% concentration of Ni; and Fe: 0.007 mass% to 0.25 mass%; P: 0.001 mass% to 0.2 mass%; C: 0.0001 mass% to 0.001 mass%; Cr: 0.001 mass% to 0.3 mass%; and Zr: 0.001 mass% to 0.3 mass%,