In order to clarify the magnetic property of GeCo2O4, we grew single crystals and performed the X-ray diffraction, magnetic susceptibility and magnetization measurements. We observed the anomaly corresponding to the antiferromagnetic transition at TN=20.8K in the susceptibility measurements. We confirmed that a structural phase transition from cubic to tetragonal symmetry occurs accompanied by the antiferromagnetic transition by the X-ray powder diffraction analysis. In the magnetization measurements up to 12T we observed step-like anomalies below TN. This behavior depends on the field direction, indicating the existence of the magnetic anisotropy in high fields. The field versus temperature phase diagrams were determined along the field directions of cubic [100], [110] and [111].