[en] The betatron functions of the storage ring of the Photon Factory at KEK were measured. The measured values of the betatron functions agree with their theoretical values very well. When the vertical wiggler is excited, tune shifts are produced and the betatron functions are distorted by about 45 % in the horizontal direction and by 30 % in the vertical direction. A simple mathematical model, in which the vertical wiggler is assumed to consist of three rectangular magnets with the sextupole field component, can explain the tune shifts and also can give a good estimate of the distortion of the betatron functions. (author)