One of problems with mobile networks is that malicious users can enter networks and launch attacks from the networks. To tackle the issues, in this paper, we propose the MSP-system: Mobile Secure Passport System. The objective of the MSP-system is to detect malicious mobile users and to prevent them from participating in mobile networks. The MSP-system is consisted of the MSP (Mobile Secure Passport) and the MSP-gateway. The MSP, which is a secure mobile device, preserves users' history information. The MSP-gateway detects malicious users by checking the history information about network activities when users try to log into networks. Thus, the MSP-system can prevent malicious users from attacking in mobile networks. Through simulation experiments, we have confirmed the effectiveness of the MSP-system.