A capillary cartridge achieves both improvement of attachability and improvement of heat dissipation performance for realizing short-time analysis. A heat dissipation body is provided between a capillary having a detection unit provided in a part thereof and a plate-like support body that supports the capillary, and temperature increase inside the capillary is suppressed by the heat dissipation body, and thereby, electrophoresis can be performed under a high voltage application condition where the amount of heat increases and analysis time is reduced. In addition, it is possible to redress complexity of an operation by reducing a fixing place at the time of attachment to only a detection unit and an electrode holder by using an integration structure in which the capillary, the supporting body, and the heat radiating body are integrated.