In a liquid crystal television, a display controller prevents burning of a liquid crystal panel due to irregularity in a synchronization signal. A counter of a liquid crystal display controller detects a period of a horizontal synchronization signal and a vertical synchronization signal. A comparator compares a count value with a predetermined minimum value Min and maximum value Max. When the count value is out of a range, a synchronization pulse generator generates a synchronization pulse at a time when the period falls within a predetermined range. A selector outputs an input synchronization signal when the period is within the range and outputs the synchronization pulse obtained from the synchronization pulse generator when the period is out of the range.