We report on the experimental observation of the spin wave spectrum control in a line-defect magnonic crystal (MC)waveguide. We demonstrate the possibility to control the forbidden frequency band (band gap) for spin waves tuning the line-defect width. In particular, this frequency may be greater or lower than the one of 1D MCwaveguide without line-defect. By means of space-resolved Brillouin light scattering technique, we study the localization of magnetization amplitude in the line-defect area. We show that the length of this localization region depends on the line-defect width. These results agree well with theoretical calculations of spin wave spectrum using the proposed model of two coupled magnonic crystal waveguides. The proposed simple geometry of MC with line-defect can be used as a logic and multiplexing block for application in the novel field of magnonic devices.