1. A service verifying system for providing a plurality of services, comprising: authentication information storing means for storing authentication information to authenticate a user permitted to utilize a first service; available service information storing means for storing information about services available to respective users; permission message information storing means for, on the occasion of permitting utilization of a second service different from the first service, storing message information based on a permission message to distinguish a permission of the utilization thereof; first message receiving means for receiving a message according to an authentication method of a first service; authenticating means for verifying the message received by the first message receiving means, based on the authentication information in the authentication information storing means, to identify a user of the first service and authenticate whether the first service is available to the user; other service utilization request receiving means for receiving a utilization request for utilization of the second service, which is transmitted from the user authenticated to utilize the first service by the authenticating means; other service availability determining means for, on the occasion of receiving the utilization request by the other service utilization request receiving means, determining whether the second service is available to the user, based on the information in the available service information storing means; permission message information updating means for, when the other service availability determining means determines that the second service is available, enabling the message information based on a permission message in the permission message information storing means; permission response transmitting means for, when the other service availability determining means determines that the second service is available, transmitting a permission response based on the permission message; second message receiving means for receiving a message based on the permission response; service provision propriety determining means for verifying determines whether the second service is providable, based on the message received by the second message receiving means and the message information in the permission message information storing means; and permission message status releasing means for, when the service provision propriety determining means determines that the second service is providable, permitting utilization of the second service and disabling the message information in the permission message information storing means.