Disclosed are a high-strength Ni-base alloy, a method of producing the Ni-base alloy, and a method of recovering a member made of a degraded Ni-base alloy. It contains not more than 0.1 wt % C, not more than 50 wt % Fe, not more than 30 wt % Cr, Ti, and at least one of Nb and Al. It has been strengthened by precipitates of a γ′ phase (Ni3Al) and/or a γ″ phase (Ni3Nb). It contains also a η phase (Ni3Ti) which is thermodynamically stable in a temperature range of 800° C. to 900° C. When observed a cross-section of the Ni-base alloy, a plurality of nodes exist along each segment connecting two meeting points each of which point is defined by adjacent three crystal grains, and precipitates of the γ′ phase and/or the γ″ phase in each of crystal grains of the Ni-base alloy have an average particle size of not more than 100 nm.