A parameter modification system for a working machine that changes a parameter of control software for controlling a working machine, the parameter modification system comprising: a parameter management device that is configured to manage the parameter; a determination criterion management device that is configured to manage a determination criterion related to performance of equipment included in the working machine, the determination criterion being set in advance; an acquisition device that is configured to acquire a current state of the equipment; a determination section that is configured to determine whether current performance of the equipment satisfies the determination criterion based on a current state of the equipment acquired by the acquisition device; a calculation section that is configured to calculate a parameter that in which performance of the equipment satisfies the determination criterion based on a current state of the equipment acquired by the acquisition device and the determination criterion when the determination section determines that current performance of the equipment does not satisfy the determination criterion; and a modification section that is configured to modify the parameter managed by the parameter management device to the parameter calculated by the calculation section, characterized in that the determination criterion includes a reference value, an upper limit value, and a lower limit value, and the determination section is configured to determine that performance of the equipment does not satisfy the determination criterion when a current state of the equipment exceeds the upper limit value in a previous determination and a current state of the equipment falls below the lower limit value in a current determination, or when a current state of the equipment falls below the lower limit value in a previous determination and a current state of the equipment exceeds the upper limit value in a current determination. a parameter management device that is configured to manage the parameter; a determination criterion management device that is configured to manage a determination criterion related to performance of equipment included in the working machine, the determination criterion being set in advance; an acquisition device that is configured to acquire a current state of the equipment; a determination section that is configured to determine whether current performance of the equipment satisfies the determination criterion based on a current state of the equipment acquired by the acquisition device; a calculation section that is configured to calculate a parameter that in which performance of the equipment satisfies the determination criterion based on a current state of the equipment acquired by the acquisition device and the determination criterion when the determination section determines that current performance of the equipment does not satisfy the determination criterion; and a modification section that is configured to modify the parameter managed by the parameter management device to the parameter calculated by the calculation section, characterized in that the determination criterion includes a reference value, an upper limit value, and a lower limit value, and the determination section is configured to determine that performance of the equipment does not satisfy the determination criterion when a current state of the equipment exceeds the upper limit value in a previous determination and a current state of the equipment falls below the lower limit value in a current determination, or when a current state of the equipment falls below the lower limit value in a previous determination and a current state of the equipment exceeds the upper limit value in a current determination.