An extension unit configured to be applied to a multiple displacement sensor system comprising: an amp unit row in which one or more amp units are adjacently provided and are electrically connected to a sensor head unit for a displacement sensor such that the one or more amp units constitute an amp isolated type of displacement sensor, and a transmission line connected to each amp unit constituting the amp unit row and transmitting measurement data generated in each amp unit downstream in direction of the extension unit, wherein the extension unit is configured to be connected to and provided adjacent to the amp unit positioned at an end of the amp unit row on the downstream of the transmission line in the amp unit row, similar to the amp unit, characterized in that the extension unit comprises a storing part storing one or more process programs into which measurement algorithms are sectionalized, wherein the one or more process programs are stored in the storing part together with their identification information and execution addresses by measurement stage of a plurality of measurement stages, an execution sequence of the measurement stages being predetermined, an input part for inputting the identification information and the execution sequence of the process programs to be executed by measurement stage, a table creating part for creating a measurement process table comprising the execution sequence input by the input part and the execution addresses read by the storing part, and a measurement stage based program executing part for reading and executing one or more process programs by measurement stage based on the measurement process table. an amp unit row in which one or more amp units are adjacently provided and are electrically connected to a sensor head unit for a displacement sensor such that the one or more amp units constitute an amp isolated type of displacement sensor, and a transmission line connected to each amp unit constituting the amp unit row and transmitting measurement data generated in each amp unit downstream in direction of the extension unit, wherein the extension unit is configured to be connected to and provided adjacent to the amp unit positioned at an end of the amp unit row on the downstream of the transmission line in the amp unit row, similar to the amp unit, characterized in that the extension unit comprises a storing part storing one or more process programs into which measurement algorithms are sectionalized, wherein the one or more process programs are stored in the storing part together with their identification information and execution addresses by measurement stage of a plurality of measurement stages, an execution sequence of the measurement stages being predetermined, an input part for inputting the identification information and the execution sequence of the process programs to be executed by measurement stage, a table creating part for creating a measurement process table comprising the execution sequence input by the input part and the execution addresses read by the storing part, and a measurement stage based program executing part for reading and executing one or more process programs by measurement stage based on the measurement process table.