A semiconductor integrated circuit includes a regulator configured to stabilize a power supply voltage from a solar cell and to output the same, a voltage detection circuit configured to detect the power supply voltage from the solar cell or an output voltage from the regulator, a power-on-reset circuit configured to output a reset signal to an external digital circuit by a voltage detection signal output from the voltage detection circuit, a memory main body configured to write and read data by the power supply voltage from the solar cell or the output voltage from the regulator.