PURPOSE: To reduce the necessary capacity of a retrieving work buffer an at the same time to improve the retrieving speed.

CONSTITUTION: A numeric character comparison part 13 compares the numerical character code of the text data received from a text code identifying part 12 with the numeric character code of the conditional numerical data received from a conditional numeric data reading part 18 to decide the difference of value between both data. The result of this comparison is given to a text code investigating part 10, a conditional numerical skip part 22, a conditional numerical substitution part 24, and a deciding part 20 respectively. The part 22 skips the numeric character data to be read out of a conditional numerical data holding part 16 next by an amount equal to one digit when the numeric character code is larger than the numeric character data. The part 24 substitutes the numeric character data to be read out of the part 16 next for the prescribed numerical value larger than the maximum numerical value equivalent to one digit that can be obtained out of a text when the numeric character code is different from the numeric character code. Then the part 20 decides whether each numerical data satisfies the prescribed numerical conditions or not.