A treatment device that shortens the time period until healing is determined even when a bone defect or a root apex lesion is generated in an apical area. The treatment device includes a file holder, a high-frequency signal generating circuit, and a control circuit. The file holder holds a file to be located in the site to be treated. The high-frequency signal generating circuit passes a high frequency current through the file. The control circuit controls a frequency of the high frequency current to be passed through the file from the high-frequency signal generating circuit. The control circuit controls the frequency of the high frequency current to be passed through the file within a range of 1.001 MHz to 11.700 MHz.