kinds of circuits built in an ic are pablicly known however as compared with them the circuit construction as shown in fig1 for example is favorable which was filed by the applicant as a specification of japanese patent application no 87417 77 on july 22 1977 in fig1 33 is a v dd supply terminal and 34 is a control terminal for supplying a control pulse to the gate of a mosfet switch 32 for operating the constant current circuit and discharging it in the constant current circuit there is utilized the fact that the drain current in the saturation region of the enhancement type mosfet is substantially constant independently of the drain voltage this constant current circuit consists of a constant current output circuit 35 and its bias circuit 36 the constant current output circuit 35 comprises two enhancement type mosfet 39 s 351 and 352 connected in series between the output terminal and the earth the bias circuit 36 operates the enhancement type mosfet 39 s 351 and 352 in the saturation region and is formed by a first voltage division circuit consisting of the depletion type mosfet 361 and the enhancement type mosfet 362 and a second voltage division circuit consisting of the depletion type mosfet 363 and the enhancement type mosfet 364 the constant voltage of the first voltage division circuit is applied to the gate of the enhancement type mosfet 352 while the constant voltage of the second voltage division circuit is applied at the gate of the enhancement type mosfet 351 these constant voltages are set to operate the enhancement type mosfet 39 s 351 and 352 in the saturation region the variation of the voltage at the connection point.