In an automatic correction process, automatic correction processing portions 60 are connected to a set reference channel and target channels, respectively, so that test signals will be input to the automatic correction processing portions 60, respectively. A rise detection portion 60a detects a rise in a test signal input to a corresponding channel, so that a value counted by a sample counter 61 is latched by a latch 60b at the rising timing of this test signal. In accordance with a difference between the counted value latched to the reference channel and the counted value latched to the target channel, a time difference is calculated. In accordance with the time difference, a delay time set for a channel delay means of the target channel is automatically corrected.