To provide an oscillation circuit that functions reliably independently of the property of a resonator and can provide a large oscillation amplitude in spite of a slight power input.

An attenuation equalization circuit (ENT) for amplitude control provided with connection terminals (K1, K2) for connection of a resonator(RES) in this oscillation circuit has either of adjustable gain and adjustable mutual conductance and at least either of them can be controlled depending on the oscillation amplitude. Furthermore, the control variable of at least either of the gain and the mutual conductance is kept constant over all oscillation amplitude values independently of at least either of an instantaneous voltage and an instantaneous current at the connection terminals (K1, K2) of the attenuation equalization circuit (ENT) for amplitude control.