In a MG control device, a standard voltage calculation part calculates a d-axis standard voltage Vd_std and a q-axis standard voltage Vq_std to be supplied to a MG. A first magnetic flux change amount estimation value calculation part calculates a first magnetic flux change amount estimation value Δϕ1 based on a deviation of a specific value from the q axis standard voltage Vq_std, where the specific value is obtained by multiplying a ratio (Vd_std/Vd_real) with a q-axis real voltage Vq_real, where Vd_real represents a d-axis real voltage. A second magnetic flux change amount estimation value calculation part calculates a second magnetic flux change amount estimation value Δϕ2 based on a deviation of the q-axis real voltage Vq_real from the q-axis standard voltage Vq_std. The calculation switching part selects one of Δϕ1 and Δϕ2 based on an operation state of the MG.