A programmable logic controller includes a device that stores therein data, an authentication-information storage unit that stores therein authentication information, an authentication function unit that performs a user authentication based on the authentication information, and an encryption filter that has a plurality of encryption patterns. When writing of data to the device is requested, the authentication function unit performs the user authentication. When the user authentication is successful, the encryption filter performs the encryption processing to the data with the encryption pattern set in advance by the user to write the data to the device, and when the user authentication fails, the encryption filter performs the encryption processing to the data with one of the encryption patterns that is different from the encryption pattern set in advance by the user to write the data to the device.