PROBLEM TO BE SOLVED: To provide a technique capable of simply and robustly measuring the thickness of a body to be measured.SOLUTION: A thickness measuring method includes: a delay time setting step (S104) of setting a delay time to each element: a beam forming step (S105) of synthesizing a reception signal output by each element by delaying it by the delay time set to each element, to form a synthetic beam signal a scan step (a loop from S104 to S105) of performing the beam forming step a plurality of times by changing the delay time to form a plurality of reception beam signals and a thickness detection step (S107) of detecting the thickness of the cortical bone based on the plurality of reception signals.
