It is important task for recovering of Cs from the contaminated area caused by the accident at the Fukushima Daiichi Nuclear Power Station. We developed a highly efficient Cs adsorbent by radiation grafting of ammonium 12-molybdophosphate (AMP) and crosslinking of grafted chains with a suitable crosslinker at the same time. As a result of the optimizaion, the Cs adsorbent with 1 mol\% of polyethylene glycol dimethacrylate satisfied the specification as a water purifier. The resultant grafted Cs adsorbent could work to maintain the highly performance of Cs removal in the standard pH range for drinking water (from pH 5.8 to 8.6) and even in the presence of coexisting ions such as K, Ca, Mg, and Na.