To provide a data logger system provided with a graph scale compression function capable of securing the reproducibility of the graph display even if the compressibility is changed, without losing the changing point of the digital signal in the compression process.

The data logger provided with the graph scale compression function of this invention composed of: a detector 3; a time controller 4; a temporally memory 5; a main memory 6; a display part 9; an input part 10; an operation part 2 for controlling theses parts; a monitoring object 7 connected with a cable 8; and a logical operation part 11 for operating the logical sum or logical product of the accumulated data by the additional information input by an input part 10.