It is well known that the biography of Bernini written by Filippo Baldinucci and another by his son, Domenico Bernini, are the most important sources for studies on Bernini. In recent years, the interests in these two biographies have grown tremendously and scholars have carefully studied them from various angles. Domenico's biography of Bernini translated to English by Franco Mormando, and the collection of critical essays on Bernini's biographies edited by Maarten Delbeke and others, are the most significant results of these studies. In this essay, the author discusses characteristics of the two biographies, centered around Portrait of Costanza Bonarelli. First, the author translates the notable documents concerning the scandal of Bernini and Costanza Bonarelli into Japanese, and sums the historical facts. Then the author introduces Costanza’s early life and her whereabouts after the scandal, based on the study published by Sarah McPhee on Costanza Bonarelli. Taking into consideration of all the historical facts and descriptions of the scandal by Baldinucci and Domenico, the author discusses intentions and characteristics of two biographies and their authors. Baldinucci was well informed about the scandal but did not mention it, whereas, Domenico wrote in details tying to his father’s honor in the form of Pope’s pardon. The difference in these descriptions reveals characteristics of eachof the biographies.