In a television signal frame number converter for converting an input television signal having a first frame number per second into an output television signal having a second frame number per second in accordance with an interpolation coefficient, a processing unit processes two successive frames of the input television signal by a frame interpolation process to produce a processed signal. A memory unit memorizes the processed signal in synchronism with a write-in address signal given by a first frame synchronizing signal of the input television signal and is read out by a read-out address signal given by a second frame synchronizing signal of a reference television signal having the second frame number per second. The converter determines the interpolation coefficient in accordance with a time interval between a write-in start timing of the memory unit and a read-out start timing of the memory unit.