This energy treatment tool (2) is provided with a first gripping piece (15) and a second gripping piece (16). A blood vessel (X1) can be sealed if the blood vessel (X1) is gripped between the gripping pieces (15, 16), and a high-frequency current is passed through the blood vessel (X1) at a first voltage value (V1) for a first period of time (t1) via a first electrode (27) on the first gripping piece (15) and a second electrode (28) on the second gripping piece (16). The second gripping piece (16) is provided with a pressure sensor (42). The pressure sensor (42) detects a parameter related to a load (σ) for attempting to open the second gripping piece (16). If the load (σ) is equal to or greater than a threshold value (σth), the output voltage (V) is set to a second voltage value (V2) that is lower than the first voltage value (V1), and the blood vessel (X1) is sealed over a second period of time (t2) that is longer than the first period of time (t1). Accordingly, sealing performance with respect to the blood vessel (X1) can be maintained, even if a tensile force is being exerted on the blood vessel (X1), and the load (σ) is high.