The transistor suffers the variation caused in threshold voltage or
mobility due to gathering of the factors of the variation in gate
insulator film resulting from a difference in manufacture process or
substrate used and of the variation in channel-region crystal state. The
present invention provides an electric circuit having an arrangement such
that both electrodes of a capacitance element can hold a gate-to-source
voltage of a particular transistor. The invention provides an electric
circuit having a function capable of setting a potential difference at
between the both electrodes of the capacitance element by the use of a
constant-current source.