PURPOSE: To provide an oscillation circuit in which a low power consumption can be obtained, and the rising of an oscillation is quick by connecting transistors which are turned off at the time of the rising of the oscillation in parallel with resistances inserted between a CMOS invertor and a power source.

CONSTITUTION: A transistor Tr 9 being a switch at a power source VDD side and a transistor Tr 10 being the switch at the power source VSS side are turned on until the rising of the oscillation. Then, a power supply voltage is impressed on a CNOS invertor constituted of a PchTr 7 and an NchTr 8 as it is without being allowed to pass through a resistance 12 for reducing through currents at the VDD side and a resistance 13 for reducing through currents at the VSS side. Thus, the CMOS invertor is driven with the 100% capability, the oscillation is judged by a comparator 11, and the Tr 9 and 10 are turned off at the time of the rising of the oscillation. Then, the power source is supplied through the resistances 12 and 13 to the CMOS invertor, and the CMOS invertor is driven with the decreased drive capability. Therefore, the oscillation circuit which is low in power consumption and the rising of the oscillation is quick can be obtained.