  We performed millimeter observations in CO lines toward the supernova remnant
(SNR) HB 3. Substantial molecular gas around -45 km s^-1 is detected in the
conjunction region between the SNR HB 3 and the nearby W3 complex. This
molecular gas is distributed along the radio continuum shell of the remnant.
Furthermore, the shocked molecular gas indicated by line wing broadening
features is also distributed along the radio shell and inside it. By both
morphological correspondence and dynamical evidence, we confirm that the SNR HB
3 is interacting with the -45 km s^-1 molecular cloud (MC), in essence, with
the nearby H II region/MC complex W3. The red-shifted line wing broadening
features indicate that the remnant is located at the nearside of the MC. With
this association, we could place the remnant at the same distance as the W3/W4
complex, which is 1.95 +- 0.04 kpc. The spatial distribution of aggregated
young stellar object candidates (YSOc) shows a correlation to the shocked
molecular strip associated with the remnant. We also find a binary clump of CO
at (l = 132.94 deg, b = 1.12 deg) around -51.5 km s^-1 inside the projected
extent of the remnant, and it is associated with significant mid-infrared
(mid-IR) emission. The binary system also has a tail structure resembling the
tidal tails of interacting galaxies. According to the analysis of CO emission
lines, the larger clump in this binary system is about stable, and the smaller
clump is significantly disturbed.
