A spectrum analyzer comprising various components. In the analyzer, a high-frequency signal processing circuit (1, 2, 3) frequency-converts an object signal including waves recurring for a short period of time, into an intermediate-frequency signal, by using a local oscillation signal swept continuously over a desired range of frequencies, and thereby outputs a frequency spectrum of the object signal. A demodulator demodu­lates the frequency spectrum output by the (4) high-­frequency signal processing circuit (1, 2, 3). A selection signal supplying section (8) supplies a selection signal for selecting that portion of the spectrum output by the demodulator (4), which lies waves to be analyzed. A control section (6) outputs said portion of the spectrum output by the demodulator (4), in accordance with the selection signal output from the selection signal supplying section (8). A display (7) displays the frequency spectrum output by the control section. A sweep control section (5) causes the high-­frequency signal processing circuit (1, 2, 3) to sweep the local oscillation signal repeatedly, each time for a period which is not an integral multiple of the cycle period of the selection signal.