A tomographic image generation device includes a projection image acquisition section configured to acquire plural projection images obtained by radiating radiation onto a breast in sequence from plural radiation angles and by performing imaging at each of the plural radiation angles; a mammary gland density acquisition section configured to acquire a mammary gland density of the breast; a derivation section configured to derive a slice thickness that decreases as the mammary gland density acquired by the mammary gland density acquisition section increases; and a generation section configured to generate a tomographic image at the slice thickness derived by the derivation section based on the plural projection images acquired by the projection image acquisition section.