With a CD laser, a focusing search is carried out to detect a value CD-FE(pp) which is a difference between a maximum value and a minimum value of a focusing error signal, and to detect a value CD-AS which is a maximum value of a full-added signal. With a DVD laser, the focusing search is carried out to detect a value DVD-FE(pp) which is a difference between a maximum value and a minimum value of the focusing error signal, and to detect a value DVD-AS which is the maximum value of a full-added signal. The value that DVD-FE(pp) is divided by DVD-AS(max), is divided by the value that CD-FE(pp) is divided by CD-AS(max). According to whether the computed result by division is larger or not than a threshold value, it is determined whether the disk 100 is of a CD standard or of a DVD standard.