A flexible wiring board for a magnetic head assembly is provided. A motion-imparting member is provided at the drum supporting member, movably relative to the drum supporting member and is configured to act on an engageable portion of each exposure unit to thereby cause the exposure unit to move to the exposure position or to the retreating position. Since the thickness of the object layer is analyzed based on the spectrum area instead of using the half value width of the spectrum, the analysis processing can be rapidly performed and the accuracy of the analysis can be improved. The opaque film does not transmit the exposed light. Similarly, the information regarding long-term variations in workload is determined.