A luminance interspersion type waveform display apparatus arranged in such a manner that a supplied waveform signal is successively sampled and amplitude data of each time-base address corresponding to a display frame is stored by a memory. The serial dot data processor successively reads the amplitude data of the adjacent time-base address from the memory. The serial dot data processor connects the amplitude data items so as to linearly intersperse the luminance in synchronization with a clock. The apparatus contains a bit map memory having two or more regions which can be shifted and written in each amplitude address of the respective time-base address in synchronization with the clock input. The two or more regions are capable of being simultaneously set to a reading mode and a writing mode. These modes are alternately switched so that when the serial dot data is written in one region in a direction perpendicular to the direction of the time-base address, another region is read in the direction of the time-base address and the waveform is displayed on a waveform display apparatus by raster scanning.