We study thermal excitations of the pseudospin soliton phase in the bilayer quantum Hall (QH) state at total Landau level filling factor ν = 1. Near the commensurate-incommensurate phase transition point in the bilayer ν = 1 QH state, we have found anomalous magnetotransport phenomena, such as the magnetoresistance peak and its anisotropic transport, which are ascribed to the formation of the pseudospin soliton phase (A. Fukuda et al., Phys. Rev. Lett. 100, 016801 (2008)). In this work, we elaborately measured activation energy gap Δ of the bilayer ν =1 QH state. Δ shows a broad minimum in the pseudospin soliton phase between the commensurate and incommensurate phase. We suggest that the minimum in Δ is due to collective modes of the pseudospin solitons forming a lattice.