  There is much observational evidence that active star formation is taking
place in the HII regions Sh 2-255 -- 257. We present a photometric study of
this star forming region (SFR) using imaging data obtained in passbands from
the optical to the mid-infrared in order to study the star formation process. A
total of 218 members were identified using various selection criteria based on
their observational properties. The SFR is reddened by at least E(B-V) = 0.8
mag, and the reddening law toward the region is normal (R_V = 3.1). From the
zero-age main sequence fitting method it is confirmed that the SFR is 2.1 +/-
0.3 kpc from the Sun. The median age of the identified members is estimated to
be about 1.3 Myr from comparison of the Hertzsprung-Russell diagram (HRD) with
stellar evolutionary models. The initial mass function (IMF) is derived from
the HRD and the near-infrared (J, J-H) color-magnitude diagram. The slope of
the IMF is about Gamma = -1.6 +/- 0.1, which is slightly steeper than that of
the Salpeter/Kroupa IMF. It implies that low-mass star formation is dominant in
the SFR. The sum of the masses of all the identified members provides the lower
limit of the cluster mass (169M_sun). We also analyzed the spectral energy
distribution (SED) of pre-main sequence stars using the SED fitting tool of
Robitaille et al. and confirm that there is a significant discrepancy between
stellar mass and age obtained from two different methods based on the SED
fitting tool and the HRD.
