A tilt detecting apparatus is provided with: a first changing device for changing a focus position of laser light in a lamination direction of recording layers; a second changing device for changing the focus position in a radial direction of the information recording medium; and a tilt detecting device for detecting an amount of tilt, on the basis of a photo-detection signal. Its controlling device controls the first changing device to set the focus position onto one recording layer, controls the second changing device to displace the focus position to a j-th radial direction position (wherein j is a natural number) on the information recording medium, and controls the tilt detecting device to detect the j-th amount of tilt for the one recording layer. Then, it controls the first changing device to set the focus position onto another recording layer while the focus position is fixed at the j-th radial direction position and controls the tilt detecting device to detect the j-th amount of tilt for the another recording layer. Then, it controls the second changing device to displace the focus position to a j+1-th radial direction position on the information recording medium while the focus position is fixed on the another recording layer and controls the tilt detecting device to detect the j+1-th amount of tilt for the another recording layer.