The invention provides an optical disk apparatus and an optical disk that are applicable to a multilayer optical disk, and enable tilt detection with a high precision. The optical disk has a transparent planar disk base member, a recording layer formed on the disk base member, and a reflecting layer in a certain positional relation to the recording layer. The optical disk apparatus includes a laser pointer 61 for irradiating a laser beam onto the recording layer of the optical disk by way of the disk base member to form a focusing spot on the recording layer, a photo-sensor array 6G for receiving a reflected beam from the reflecting layer, and an aberration mode detecting circuit 6H for detecting tilt of the optical disk by using an output from the photo-sensor array 6G.