We report Swift Burst Alert Telescope (BAT) observations of the X‐ray Flash (XRF) XRF 050416A. The fluence ratio between the 15–25 and 25–50 keV bands of this event is 1.1, thus making it the softest gamma‐ray burst (GRB) observed by BAT so far. The spectrum is well fitted by the Band function with Epeakobs of 15.6−2.7+2.3 keV. Assuming the redshift of the host galaxy (z=0.6535), the isotropic‐equivalent energy Eiso and the Epeak energy at the GRB rest frame (Epeaksrc) of XRF 050416A are not only consistent with the correlation found by Amati et al. and extended to XRFs by Sakamoto et al., but also fill‐in the gap of this relation around 30–80 keV range of Epeaksrc. This result tightens the validity of the Epeaksrc−Eiso relation form XRFs to GRBs.