PURPOSE: To minimize a storage area to be used and to improve the sampling speed, by performing leel discrimination with an address of storage location of a sampling data, in reading data storage system of a bar code reader.

CONSTITUTION: In sampling a continuous signal substantially taking the 1st or 2nd level only at a prescribed period and storing the signal to a stoage device M, sampling numbers n1Wn3 from a changing point produced before to that produced afterward as to changing points t1Wt5 of a sampling data value are counted and the count value is sequentially stored to storage positions m1Wm4 in a storage device M, and a discrimination flag (d) representing whether addresses a1Wa4 of the storage position started with the storage of the sampling data are an odd or an even number, is stored and the discrimination of the 1st or 2nd level is made depending whether the addresses a1Wa4 of the storage position of the sampling data is an even or an odd number.