We developed a new measurement method for the isometric knee extensor strength with a hand-held dynamometer (HHD). The purpose of this study was to assess the clinical utility of the new method by examining the interrater reliability between male and female rater, validity and simplicity. The subjects were 31 community-dwelling elderly people (9 male, 22 female, mean age 81.6±6.1 years) who were receiving a day-care rehabilitation program. Their isometric knee extensor strength were measured three times by this method and the belt method that fixed a HHD by a belt. The time to finish the measurement was recorded under the condition that the rater was masked. As a result, intraclass correlation coefficient (ICC), which represents interrater reliability between male and female rater, was 0.96. There were no significant differences in the measurement values between this method (male and female rater) and the belt method. ICCs of the belt method were 0.89 in male rater and 0.90 in female rater. The time to finish the measurement by this method was 2 minutes and 12 seconds (± 40 second) on average, which was significantly shorter than the belt method (p<0.05). From these results, the reliability, validity and simplicity for the frail elderly of this new method were considered acceptable.