A semiconductor memory device, which can reduce consuming power and perform a power-off operation correctly, is provided. A flash memory of the invention includes: a low-power-voltage detection circuit detecting that a supply voltage drops to a given voltage; a high-accuracy voltage detection circuit detecting that the supply voltage drops to the given voltage; and a controller selecting the high-accuracy voltage detection circuit when an internal circuit is in an operation state, selecting the low-power-voltage detection circuit when the internal circuit is in a standby state, and performing a power-off operation in response to a detection result of the low-power-voltage detection circuit or the high-accuracy voltage detection circuit.