For lidar measurements of stratospheric aerosols; signal-induced noise (SIN) from a photomultiplier (PMT) has been a problem of particular interest. In this paper, lidar signals affected by the PMT are simulated after a long tail with a decay time of about 200 microsec is found in the PMT's response to an impulse-like light exposure. Computer simulation quantitatively revealed that the SIN caused by the delayed response became greater than the real signal at high altitudes. Based on the results of the simulation, a proposal was made to find a practical method for identifying and removing the SIN from the actual lidar signals. In addition, an improved method for the lidar signal calibration was proposed, taking into account the systematic noise component, including background light as well as SIN, in formulating the clean air calibration (the matching method). The validity of the proposed methods was demonstrated by using them both with an actual lidar signal and a simulated lidar signal with SIN.