An interlock for a slider incorporates a cover that moves between a covered position and an uncovered position. A coordinate inputting apparatus includes a pen for transmitting an ultrasonic wave and a coordinate inputting apparatus for inputting coordinate positions of the pen based on a propagation time of the ultrasonic wave transmitted by the pen and received by a plurality of ultrasonic wave receivers. To manufacture acrylic acid, a gaseous mixture of acrolein and of water vapor and, if appropriate, of an inert gas is passed over a solid composition of formula, to conduct the redox reaction by operating at a temperature of 200 to 500 C. The camera main body includes a held portion that is located off the optical axis and configured to be held by an operator, and a monitor on its outer surface.