A semiconductor device in which consumption of power attendant on a leakage current in a block where the power is turned on and off intermittently is reduced. In the semiconductor device according to the present invention, an error check necessity judgment circuit judges on notification from an error check necessity notification circuit located in a block where the power is not disconnected whether an error check must be made, and an error check execution circuit makes an error check on data loaded from an external memory at the time of a boot in accordance with the judgment of the error check necessity judgment circuit. An error check cannot completely be omitted. Therefore, to ensure the reliability of a system, an error check is forcedly made once whenever a boot is performed times set by an error check interval setting circuit. This shortens intermittent operation time by time taken to make an error check, resulting in a reduction in consumption of power attendant on a useless leakage current.