A glass ceramic substrate includes: an inner layer part having a first thermal expansion coefficient; and a surface layer part having a second thermal expansion coefficient smaller than the first thermal expansion coefficient. The inner layer part contains a first glass matrix and flat alumina particles. The flat alumina particles are dispersed in the glass matrix in a direction in which individual thickness directions are substantially perpendicular to a surface direction of one of main surfaces of the inner layer part. Further, a mean aspect ratio of the flat alumina particles is 3 or more in one of cross sections along the thickness directions of the flat alumina particles out of cross sections of the inner layer part.