A treatment system can include a treatment instrument with an operation input element that has a magnet; and a sensor that detects a parameter that changes with a movement of the magnet together with the operation input element based on an operation of the operation input element. The treatment system can also include a control apparatus that can control the supply of electrical energy to the treatment instrument for operation of the treatment instrument. The control apparatus includes a processor that can determine a relationship between a change in a distance between the sensor and the magnet and a change in the parameter, and to set, based on the relationship, a threshold for switching between an ON state and an OFF state of the supply of the electrical energy to the treatment instrument.