A synchronous-motor control apparatus, comprising: estimation means for estimating magnetic-pole position of a rotor, said synchronous-motor control apparatus separating a motor-current detection value into a d-axis current detection value and a q-axis current detection value on d-q-axes orthogonal rotation coordinate axes, said coordinate axes rotating in synchronization with an estimated magnetic-pole position outputted by said magnetic-pole position estimation means, and generating a voltage instruction value v dc * and a voltage instruction value v qc * for a power converter independently of each other, said voltage instruction values being defined on said coordinate axes, characterized in that when letting said d-axis current detection value be i dc, said q-axis current detection value be i qc, said parameters for representing said motor characteristics be a parameter K 4 for representing magnitude of a q-axis inductance value of said motor which is to be employed as said control target, a parameter K 5 for representing a cross-coupling degree of said q-axis inductance from said d-axis current, a parameter K 6 for representing a saturation degree of said q-axis inductance relative to said q-axis current, and a parameter I 0 for representing a current for minimizing said cross-coupling degree of said q-axis inductance from said d-axis current, and an axis-error estimation value be Δθ, a q-axis inductance component L q (i dc, i qc, Δθ) of said motor used in said magnetic-pole position estimation means is calculated using the following expression: L q i dc, i qc, Δ θ = K 4 1 + K 5 | i dc cosΔ θ − i qc sinΔ θ + I 0 | + K 6 | i dc sinΔ θ + i qc cosΔ θ | estimation means for estimating magnetic-pole position of a rotor, said synchronous-motor control apparatus separating a motor-current detection value into a d-axis current detection value and a q-axis current detection value on d-q-axes orthogonal rotation coordinate axes, said coordinate axes rotating in synchronization with an estimated magnetic-pole position outputted by said magnetic-pole position estimation means, and generating a voltage instruction value v dc * and a voltage instruction value v qc * for a power converter independently of each other, said voltage instruction values being defined on said coordinate axes, characterized in that when letting said d-axis current detection value be i dc, said q-axis current detection value be i qc, said parameters for representing said motor characteristics be a parameter K 4 for representing magnitude of a q-axis inductance value of said motor which is to be employed as said control target, a parameter K 5 for representing a cross-coupling degree of said q-axis inductance from said d-axis current, a parameter K 6 for representing a saturation degree of said q-axis inductance relative to said q-axis current, and a parameter I 0 for representing a current for minimizing said cross-coupling degree of said q-axis inductance from said d-axis current, and an axis-error estimation value be Δθ, a q-axis inductance component L q (i dc, i qc, Δθ) of said motor used in said magnetic-pole position estimation means is calculated using the following expression: L q i dc, i qc, Δ θ = K 4 1 + K 5 | i dc cosΔ θ − i qc sinΔ θ + I 0 | + K 6 | i dc sinΔ θ + i qc cosΔ θ |