PURPOSE: To obtain an amplifier circuit in which the destruction of a transistor used in a circuit can be reduced, and with satisfactory measuring sensitivity even when a signal source is a current type signal source, and not requiring an adjusting means for a gate voltage.

CONSTITUTION: This circuit is provided with a current mirror circuit or constant current circuit in which a #1 transistor 11, an intermediate terminal 4, and a #3 transistor 13 are connected in series between a power source terminal 1 and a signal input terminal 2, and also, a #2 transistor 12, a signal output terminal 5, and a #4 transistor 14 are connected in series between the power source terminal 1 and a signal input terminal 3, and a current ratio of transistor 11 to 12 is set at 1:n, and a current mirror circuit in which a current ratio of transistors 13 to 14 is set at the same ratio as 1:n.