The present invention provides a portable optical reader, an optical reading method using the portable optical reader and a computer program capable of detecting a high possibility of a reading error and notifying a user of a possibility of a reading error. A character string as a reading target is imaged and a character string is recognized based on the captured image. A plurality of reading formats defining an attribute of the character string is stored, and a first reading format matched with the recognized character string among a plurality of stored reading format is searched. Among the plurality of stored reading formats, a second reading format in which a character string matched with the first reading format as a partial character string is searched. Based on the search result, a possibility of a reading error regarding the recognized character string is notified.
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