The present invention provide a compound of the formula: 1 wherein X and X' are the same or different and each represents a hydrogen atom, etc.; R.sup.1 and R.sup.2 are the same or different and each represents a hydrogen atom, etc.; R.sup.3 represents a hydrocarbon group optionally having substituents, etc.; R.sup.4 represents a hydrogen atom, etc.; Y and Ya are the same or different and each represents a bond or a spacer having a main chain of 1 to 8 atoms; Z and Za are the same or different and each represents a hydrogen atom, etc.; or a salt thereof or a prodrug thereof, having a somatostatin receptor binding inhibitory activity and is useful for preventing and/or treating diseases associated with somatostatin.