A piezoelectric/electrostrictive ceramic sintered body has a microstructure in which a matrix phase and an additional material phase having different compositions coexist and the additional material phase is dispersed in the matrix phase. A residual strain ratio of the additional material phase alone is larger than a residual strain ratio of the matrix phase alone. The matrix phase and the additional material phase have a composition in which a Mn compound containing Mn atoms of 0 parts by mol or more and 3 parts by mol or less and a Sr compound containing Sr atoms of 0 parts by mol or more and 1 part by mol or less are contained in a composite of 100 parts by mol represented by a general formula {Liy(Na1-xKx)1-y}a(Nb1-z-wTazSbw)O3, where a, x, y, z and w satisfy 0.9≦a≦1.2, 0.2≦x≦0.8, 0.0≦y≦0.2, 0≦z≦0.5 and 0≦w≦0.1, respectively.