Cleaning system for telephone number list

A cleaning system for a telephone number list comprising:

• loading means for loading a telephone number list to be subject to a cleaning process, in a memory;
• calling means for reading out each telephone number contained in said telephone number list stored in said memory and transmitting a dialing signal corresponding to said each telephone number to a public telephone network;
• line monitoring means for monitoring reaction on the line with respect to the transmission of the dialing signal by said calling means;
• effectiveness judging means for making judgment of an effective telephone number and disconnecting the line immediately when a ring tone is detected within a predetermined period, or when an off-hook signal is detected prior to detection of a ring tone;
• voice recognition means which is active when none of said ring tone, said off-hook signal and said busy tone is detected by said line monitoring means within a given period after initiation of call, and for recognizing a specific voice signal on the line and disconnecting the line thereafter;
• changing number recognizing means for making judgment of effectiveness of a new telephone number contained in a guidance message when the guidance message announcing change of the telephone number is detected by said voice recognition means;
• null telephone number discriminating means for making judgment that the telephone number checked is null when the guidance message announcing the change of the telephone number is not detected by said voice recognition means;
• and
• outputting means for generating output lists with distinguishing the effective telephone numbers and the null telephone numbers on the basis of the results of discrimination by said effectiveness judgment means, said changing number recognizing means and said null telephone number discriminating means.