The present invention relates to a high entropy alloy having more improved mechanical properties by controlling contents of additive elements in a NiCoFeMnCr 5-element alloy to control stacking fault energy, thereby controlling stability of a γ austenite phase to control a transformation mechanism, wherein the stacking fault energy is controlled in a composition range of NiaCobFecMndCre (a+b+c+d+e=100, 1≤a≤50, 1≤b≤50, 1≤c≤50, 1≤d≤50, 10≤e≤25, and 77a−42b−22c+73d−100e+2186≤1500), and thus, the γ austenite phase exhibits a twin-induced plasticity (TWIP) property or a transformation induced-plasticity (TRIP) property in which the γ austenite phase is subjected to phase transformation into an ε martensite phase or an α′ martensite phase, under stress, thereby having improved strength and elongation at the same time to have excellent mechanical properties.