Powder neutron diffraction revealed that delafossite CuFeO2 exhibits successive magnetic transitions at T(N1) = 16 K and T(N2) = 11 K. The low-temperature ordered phase and the high-temperature ordered phase have collinear spin structures with an orthorhombic magnetic unit cell (square-root 3a x 2a x 2c) and a monoclinic unit cell (square-root 7a x square-root 7a x 2c), respectively. The successive magnetic transitions are discussed in terms of the spin frustration.