We investigated the accuracy and operability of two ultrasound devices for the bladder. The study included 232 adult patients who underwent surgery at our hospital. Before surgery, a nurse measured the amount of urine in the bladder using Lilium α-200® and Bladder Scan BVI 6100®. The amount was measured accurately later using a catheter. The measurements by the devices were compared with the amount measured by the catheter. Both Lilium and Bladder Scan had high accuracy (correlation coefficient for Lilium is 0.56 [95% CI : 0.46-0.64], and the correlation coefficient for Bladder Scan was 0.70 [95% CI : 0.63-0.76]). However, values obtained by the two devices significantly differed from the catheter measurement. The accuracy was improved by excluding patients with 0- ml readings by the two devices (the correlation coefficient for Lilium was 0.69 (95% CI : 0.61-0.76), and the correlation coefficient for Bladder Scan was 0.81 (95% CI : 0.76-0.86). Next, the operability was evaluated using a questionnaire. Both devices had high operability, but Bladder Scan was easier to operate. Based on the above, Bladder Scan had significantly higher accuracy and operability, but both devices had a sufficiently high accuracy and operability for clinical practice.