A power source device configured for an electrophoresis device employing a measurement tool including a capillary, the power source device comprising: a high voltage generation circuit configured to generate a voltage for electrophoresis; a first external terminal and a second external terminal configured to apply the electrophoresis voltage to the capillary; a polarity switching circuit including a first internal conductor connected to the high voltage generation circuit and a second internal conductor, the polarity switching circuit being configured to selectably apply a potential difference between the second internal conductor and the first internal conductor across the first external terminal and the second external terminal by application with either a forward direction polarity or a reverse direction polarity; and being characterized by a switching control circuit configured to control polarity switching of the polarity switching circuit to select either one of application with the forward direction polarity or application with the reverse direction polarity; wherein: the polarity switching circuit includes a forward direction switch pair of a first forward direction switch and a second forward direction switch, and a reverse direction switch pair of a first reverse direction switch and a second reverse direction switch; the first forward direction switch is connected between the first internal conductor and the first external terminal; the second forward direction switch is connected between the second internal conductor and the second external terminal; the first reverse direction switch is connected between the first internal conductor and the second external terminal; the second reverse direction switch is connected between the second internal conductor and the first external terminal; and the switching control circuit is configured to control the polarity switching circuit so as to make either one of the forward direction switch pair or the reverse direction switch pair exclusively conductive. a high voltage generation circuit configured to generate a voltage for electrophoresis; a first external terminal and a second external terminal configured to apply the electrophoresis voltage to the capillary; a polarity switching circuit including a first internal conductor connected to the high voltage generation circuit and a second internal conductor, the polarity switching circuit being configured to selectably apply a potential difference between the second internal conductor and the first internal conductor across the first external terminal and the second external terminal by application with either a forward direction polarity or a reverse direction polarity; and being characterized by a switching control circuit configured to control polarity switching of the polarity switching circuit to select either one of application with the forward direction polarity or application with the reverse direction polarity; the polarity switching circuit includes a forward direction switch pair of a first forward direction switch and a second forward direction switch, and a reverse direction switch pair of a first reverse direction switch and a second reverse direction switch; the first forward direction switch is connected between the first internal conductor and the first external terminal; the second forward direction switch is connected between the second internal conductor and the second external terminal; the first reverse direction switch is connected between the first internal conductor and the second external terminal; the second reverse direction switch is connected between the second internal conductor and the first external terminal; and the switching control circuit is configured to control the polarity switching circuit so as to make either one of the forward direction switch pair or the reverse direction switch pair exclusively conductive.