Compounds of the formula I:or a pharmaceutically acceptable salt thereof, wherein, R1 is a group of formula A or formula B,and X, R2, R3, R4, R5, R6, Ra and Rb are as defined herein. An optical tomographic image generation method of generating a tomographic image of an object includes: acquiring a signal; performing Fourier transform; and obtaining the tomographic image. As a result, information is provided to radio terminals in the cells neighboring the CSG cell that generally indicates that radio terminals are not to report to a respective serving base station signal quality measurements of a signal received from the CSG base station unless the radio terminal is a member of the closed subscriber group for the CSG cell. A lead wire is inserted between the restriction part and the upper portion and retained by the retainer member.