A web filtering system comprising: a first storage means configured to store URLs of websites and categories corresponding to the URLs; a server determination means (56, 58) configured to, when accepting a request for determining a category corresponding to a designated URL as a request for server determination, send a result of the determination executed using the first storage means, as a response to a requester of the server determination; a second storage means configured to store periodically delivered records constituting part of all records stored in the first storage means according to a predetermined criterion; a temporary storage means configured to temporarily store result data which is transmitted from the server determination means (56, 58) as the response to the request for the server determination; a local determination means (78, 84) configured to, when accepting a request for determining a category corresponding to a designated URL as a request for local determination, attempt the determination by first using the temporary storage means, and when capable of determining the category, send the determined category as a response to a requester of the local determination, and when not capable of determining the category, attempt the determination by using the second storage means, and when capable of determining the category, send the determined category as a response to the requester of the local determination, and when still not capable of determining the category, request the server determination means (56, 58) to execute the server determination while designating the URL, and send the category determined by the server determination means (56, 58) as a response to the requester of the local determination; and an access control means configured to, when an access request to a website is made by a user terminal, request the local determination means (78, 84) to execute the local determination while designating a URL of the website and control whether to permit the access request or not according to a category which is sent from the local determination means (78, 84) as a response. a first storage means configured to store URLs of websites and categories corresponding to the URLs; a server determination means (56, 58) configured to, when accepting a request for determining a category corresponding to a designated URL as a request for server determination, send a result of the determination executed using the first storage means, as a response to a requester of the server determination; a second storage means configured to store periodically delivered records constituting part of all records stored in the first storage means according to a predetermined criterion; a temporary storage means configured to temporarily store result data which is transmitted from the server determination means (56, 58) as the response to the request for the server determination; a local determination means (78, 84) configured to, when accepting a request for determining a category corresponding to a designated URL as a request for local determination, attempt the determination by first using the temporary storage means, and when capable of determining the category, send the determined category as a response to a requester of the local determination, and when not capable of determining the category, attempt the determination by using the second storage means, and when capable of determining the category, send the determined category as a response to the requester of the local determination, and when still not capable of determining the category, request the server determination means (56, 58) to execute the server determination while designating the URL, and send the category determined by the server determination means (56, 58) as a response to the requester of the local determination; and an access control means configured to, when an access request to a website is made by a user terminal, request the local determination means (78, 84) to execute the local determination while designating a URL of the website and control whether to permit the access request or not according to a category which is sent from the local determination means (78, 84) as a response.