An observation apparatus includes a first member 9 supporting first optical elements L1L and L1R, a second member 7 supporting second optical elements L4L and L4R and the first member via balls so as to be movable in an optical axis direction, and a biasing device 11 generating a biasing force for clamping the balls. The first and second members include guide portions 7a, 7b, 9a, and 9b engaging with first balls so as to permit a rolling motion of the two first balls 10a and 10b in the optical axis direction and prevent the first member from displacing with respect to the second member in a direction orthogonal to the optical axis direction, and ball holding portions 7c, 7d, 9c, and 9d holding second balls 10c and 10d so as to permit a rolling motion of the second balls in the optical axis direction.