To provide a PID control method of an absorption type device that stabilizes a brine outlet temperature, even if a brine flow rate is changed from a rated value.

There are defined an input heat quantity as M (%), a flow rate ratio with respect to a rated flow rate of brine as F, a difference between brine temperatures at an inlet and an outlet of an evaporator as e (°C), a proportional zone in the rated flow rate as Pr (°C), an integrated time in the rated flow rate as Tir (sec), and a differential time in the rated flow rate as Tdr (sec). Then, the input heat quantity M is PID-controlled by a following expression in which the proportional zone is set as (Pr/F), the integrated time as (Tir/F), and the differential time as (Tdr.F). M=(100/(Pr/F)).e+(1/(Tir/F))∫edt+(Tdr.F)de/dt.