A cardiac magnetic field diagnostic apparatus for evaluating intracardiac three-dimensional localization of a myocardial injury by means of cardiac magnetic field measurement and a three-dimensional localization evaluating method of myocardial injury are disclosed. A magnetic field distribution measuring instrument (1) creates magnetic field distribution data by contactless magnetic field measurement on coordinates on the breast of a subject. An arithmetic operation unit (2) computers intracardiac three-dimensional current density distribution data from the magnetic field distribution data, draws a magnetic field integral cubic diagram as a cardiac contour cubic diagram according to the three-dimensional current density distribution data, creates data to draw the three-dimensional distribution of the QRS difference, the T-wave vector, or the RT dispersion of the same subject according to the three-dimensional current density distribution data, and reconstructs it on the cardiac contour. With this, evaluation of three-dimensional localization of a myocardial injury is possible.