and r 3 indicate resistors and s indicates a normally closed type switch to be opened for example as interlocked with an engine key when it is rotated to the on position symbol t indicates a voltage reducing transformer consisting of primary coils la and lb and a secondary coil lc a voltage from a constant voltage circuit 2 is normally fed to an input end i of the oscillating circuit in the initial state as the transistor q conducts the capacitor c will be charged through the course of the primary coil lb u2192 capacitor c u2192 parallel circuits of the resistors r 2 and r 3 u2192 base and emitter of the transistor q and the electric current will flow also to the primary coil la through the collector and emitter of the transistor q when the capacitor c is charged to a predetermined value the transistor q will be cut off and at this time the electric charge of the capacitor c will be discharged through the resistor r 1 u2192 parallel circuits of the resistors r 2 and r 3 when the potential between the terminals of the capacitor c reduces to a predetermined value the transistor q will again conduct to resume charging the capacitor c with the oscillation by the above operation such pulse voltage as is illustrated will be generated at the output end o of the secondary coil l 0 of the voltage reducing transformer t and will be fed to the time indicating part 6 here the duty ratio of the oscillation determining the width of the pulse voltage can be properly set by properly selecting the values of the resistors r 1 r 2 and r 3 therefore when the switch s is opened as.