An imaging device comprises a first lens unit and a second lens unit. A
first fixed barrel of the first lens unit movably holds a first lens
frame, which holds a first lens group, in an optical-axis direction. A
second fixed barrel of the second lens unit movably holds a second lens
frame, which holds a second lens group, in the optical-axis direction.
The first and second fixed barrels are secured in series in the
optical-axis direction. The first and second lens units are adapted to be
easily assembled in series in the optical-axis direction. Misalignment of
the plural lens groups is prevented, and the first and second lens groups
are accurately and individually moved in the optical-axis direction.