A current-voltage converter, comprising an operational amplifier having an input terminal and an output terminal, a first resistor portion connected to the input terminal, and a second resistor portion provided between the input and output terminals, the input terminal and the first and second resistor portions being connected to each other, the first resistor portion being connected to a current source on a side opposite to the input terminal, the second resistor portion including a diode, the first resistor portion having a first resistance value when a current of a first current amount is supplied to the first resistor portion, and having a second resistance value smaller than the first resistance value when a current of a second current amount larger than the first current amount is supplied to the first resistor portion.