Abstract: Provided is an active pull-up circuit which comprises a MOS capacitor having one end connected to an input terminal receiving a pull-up signal, a first MOS transistor having a current path connected between the other end of said MOS capacitor and a signal line precharged, during a precharge period, up to a power source voltage level, and a second MOS transistor having a current path connected between a power source terminal and the signal line and having a gate connected to a source of the first MOS transistor. To the gate of this first MOS transistor there is applied a control voltage which, during the precharge period, is higher in level than a sum of the power source voltage and a threshold voltage of the first MOS transistor and, after the lapse of the precharge period, is substantially equal in level to the power source voltage.