1. A check system, comprising a client device ( 301 ) and a server device, wherein (a) the client device is provided with a document acquisition unit that acquires a Web document associated with a provided URL from a computer communication network, a document display unit that, once a Web document is acquired by the document acquisition unit, displays the acquired Web document, a safety information acquisition unit that acquires safety information with respect to a provided URL from the server device, a safety information display unit that, once safety information with respect to a URL contained in the Web document displayed on the screen is acquired by the safety information acquisition unit, displays the safety information near the location where the URL is displayed on the screen, an input reception unit that receives a first type or a second type instruction specifying a URL contained in the Web document displayed on the screen, and a dispatch unit that, when the first type instruction has been received, provides the URL specified by the first type instruction to the document acquisition unit, and when the second type instruction has been received, provides the URL specified by the second type instruction to the safety information acquisition unit, and wherein (b) the server device is provided with a safety information storage unit that stores a URL and safety information with respect to that URL in association with each other, and a safety information providing unit that provides the client device with safety information stored in the safety information storage unit in association with a queried URL from the client device.