An observation apparatus includes: an image capturing apparatus that includes an imaging surface and captures an image of an object to be observed; an optical system that projects an optical image of the object onto the image capturing apparatus; a focusing unit that adjusts, with reference to the optical-axis direction of the optical system, the relative positional relationship between the object and a surface optically conjugate to the imaging surface; and a processor that controls at least the image capturing apparatus and the focusing unit. The processor decides an in-focus position for the focusing unit based on a plurality of images of the object that acquired by the image capturing apparatus, the plurality of images each being an image acquired when the focusing unit is located at a different position; determines the reliability of the decided in-focus position; and when determining that the in-focus position is not reliable, moves the focusing unit sequentially to a plurality of positions and causes the image capturing apparatus to acquire, for each of the plurality of positions, a candidate image of the object.