PURPOSE: To provide a nonvolatile counter by which the reliability of stored data are always secured.

CONSTITUTION: A counter section 41 consists of 200 bits, data are written sequentially by one bit each time a distance of 1km elapses and the data are entirely erased for each 200km. An integration section 42 has a storage area by 3 words (integration values A-C) to the same data. One word of a flag section 43 is prepared for each of 3-lines of data for rewrite (integration values A-C) of the integration section 42 and one word of the flag section 43 is provided for data erasure of the counter section 41. Then the erasure for carry to the counter section 1 and rewrite to the integration section 42 are implemented only after a relevant flag word is written. Thus, even when the operation of data write/ erasure by the counter section 41 and the integration section 42 is interrupted due to various reasons midst of the operation, data and a flag word are retrieved at application of power to read correct stored data at interruption of power to obtain final data surely.