A device for generating a desired ZMP trajectory for a mobile robot includes a polynomial function coefficient group determining section (53a) which determines, by regarding the desired ZMP trajectory as a trajectory expressed by a polynomial function, a desired coefficient group composed of desired values of coefficients in respective terms of the polynomial function. The polynomial function coefficient group determining section uses a quadratic evaluation function including square values of the coefficients included in the desired coefficient group as variables and a plurality of constraint conditions each configured by a linear equality or linear inequality about the coefficients, to determine the desired coefficient group, by a solution method for a quadratic programming problem, in such a way as to minimize a value of the evaluation function while fulfilling the constraint conditions.